'FHE NAIAD FAUNA OF THE RED CEDAR RIVER, IN SOUTHCENTRAL MICHIGAN 102 838 THS Thesis {or the Degree 0‘ M. S. MICHIGAN STATE UNIVERSKTY Kenneth Jay Boss 1959 PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. a» 9.; I I, Lv, l~ml DATE DUE DATE DUE DATE DUE fEB t 51991! f NOgZQOtI 05210 iDQTlZBO I 4 , PU LL SU Is An Affirmative Action/Equal Opportunity Institution THE HAIAD FAUUA OF THE RED CEDAR RIVER, IN SOUTHCENTRAL MICHIGAN by KENNETH JAY BOSS AN ABSTRACT Of a thesis submitted to the College of Science and Arts of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology East Lansing, Hichigan 1959 Approved 1%M THESIS ABSTRACT This study was conducted to determine the Species of the naiad fauna in the Red Cedar River in southcentral Michigan. The relative richness of the fauna and distributional data pertinent to the forms was recorded. The stu y was conducted in the autumn of 1958. Eighteen stations located along the main course of the Red Cedar River were sampled. The tributaries, with the exception of three streams whose confluence forms the river, were not included in the study. Fifteen species belonging to eleven genera of the family Unionidae were found to compose the naiad fauna. Of these Elliptic dilatatus, FUSconaia flava, Anodonta grandis, Strophitus rugosus, and Lampsilis ventricosa were found to be common and widely distri- buted in the river. Others, such as Micromza iris, Actinonaias ellipsiformis, and Lasmigona compressa were found to be rare and have a restricted distribution. Since 19h0, when Dr. H. Van der Schalie sampled areas in the Red Cedar River, a decrease in the relative abundance of Nicrogza iris, Actinonaias ellipsiformis, and Alasmidonta calceolus, and an increase in the relative abundance of Anodonta grandis, Lasmigona costata, and Alasmidonta marginata have occurred. TWO areas of the river were found to be devoid of any naiad populations. These were downstream stations from Fbwlerville and East Lansing. THE E'IAIAD FAUTTA OF TfIE RED CEDAR RIVER, IN SOUTTZCET‘ETRAL I-‘IICHIGAN by KENNETH JAY BOSS A THESIS Submitted to the College of Science and Arts of fiichigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology East Lansing, Michigan 1959 Approved {@Mfi flfi ACKZ‘TO‘rF. .F .Dc-z-zzu'rs This investigation was conducted under the supervision of Professor T. w; Porter, to whom.I am indebted for his guidance, aid, and constant inspiration, without which this study could never have been realized. Grateful acknowledgment is also due to Dr. M. Hensley, of the Department of Zoology, and Dr. J. Smith, of the Department of Geology, for critically reading the manuscript. To Dr. H. Van der Schalie, of the division of malacology of the University of Michigan Museum, the author wishes to express his gratitude for advice and for confirmation of identifications. The author is also grateful to hrs. B. R. Henderson, wno aided in many ways. iii TABLE OF CONTENTS Acknowledgments. ........ ............... ..... .... ............ ........ii List of Naps........................................................iv Faunal Table.........................................................v Introduction.........................................................l Characteristics of the Red Cedar River...............................1 Description of Stations..............................................3 Key for indentification of the naiads of the Red Cedar River........ll Discussion of Species...............................................1h Elliptic d11atatus.............................................1h Fisconéiafiflava................................................15 PleurObema cordatum coccineum..................................17 Anedonta grandiS...............................................2O Lasmigona compressa............................................21 Iasmigona coststa..............................................22 AhodcntoidesiferussacianuS.....................................22 STronhi‘bus mgosusooooooooooooooococooooo‘ooooooooooooc00000000023 Masmidonta-‘WUS..HHHHH...........o..................2h msmfdonita marginaaOOOOOOOOooooococo.cooooooooooooooooooooooozs Micromya iriS..................................................30 £55 siIis siquuoidea..........................................30 IfifigsiIis ventricosa...........................................32 Actinonafias fllipsflomis......................................33 SWWCCCOOOOOOOOOOOOOOOOOOOCOOO.00.0.0000...0.00000000000000000.0.36 BibliograerOOOOOOOO00.000000...coo.ono...o000000000000000000000000037 iv MAPS COlleCting Station3.o.... ooooo 00.00.000.00. oooooooo 00000000000000.0010 Distribution Distribution Distribution Distribution Distribution Distribution Distribution Distribution of Fusconaia flava and Pleurobema cordatum coccineum...18 Of Elliptic dilatatuSOOOOOOOOOOOOOOOIO.0.00.00.00.00.0019 of Anodontoides ferussacianus and Anodonta grandis.....26 of Alasmidonta calceolus and Alasmidonta marginata.....27 of Lasmigona compressa and Lasmigona costata...........28 of Strephitus rugosus..................................29 of Lampsilis siliquoidea and lampsilis ventricosa......3h of Nicrcmya iris and Actinonaias ellipsiformis.........35 FAUNAL TABLE I. The distribution of Naiades by collecting stations in the Red Cedar murOOOOOIOOOOOOOOOOOCOOOOOO0.0.0.0000...0.0.0....13 INTRODUCTION This study of the naiad fauna of the Red Cedar River was conduct- in the autumn of 1958. The purposes of the study were to determine the species of the naiad fauna in the river, to record distributional data pertinent to the forms, and to discern the relative richness of the fauna. The collections were taken from the main course of the river and no tributaries were sampled, excepting the headwaters of the stream, which are three in number, and whose confluence forms the river proper. The problem has been primarily taxonomic and distribution- al although field data may contribute information bearing on the ecology and life history of the naiads. CHARACTERISTICS OF THE RED CEDAR RIVER The Red Cedar River is a tributary stream of the Grand River in Western Michigan, and drains a portion of the lower central part of the Southern Peninsula. The Red Cedar River forms as a confluence of the West Branch of the Cedar River and the Cedar River at the boundary line of Livingston and Ingham Counties. The Cedar River, which lies wholly within Livingston County, originates as the out- flow of Cedar Lake, Marion Township, Livingston County. A third tributary, the Middle Branch of the Cedar River, forms a confluence with the Cedar River one mile south of Fowlerville, Livingston County. In this paper, the main course of the stream refers to the Red Cedar River, which properly lies in Ingham County. The headwater tribu- taries, or upper reaches of the river, are construed to mean the West Branch of the Cedar River and the Cedar River with its tribu- tary, the Middle Branch of the Cedar River. The headwater drainage, the upper reaches of the Cedar River, is principally marsh or wet land areas, and in.many regions the stream has been channeled and straightened for the purpose of agricultural land reclamation. The Red Cedar River flows through or near the communities of Fbwlerville, Wbbberville, hfilliamston, and Ckemos before entering the East Lansing and Lansing areas and the confluence with the Grand River. The total length of the main channel is 10.25 miles. The section of the Red Cedar River, Which was surveyed, has a nmhber of tributary streams consisting of several small creeks and drainage ditches that drain an area extending approximately 11 miles on either side of the river. The total drainage area is approximate- ly 355 square miles. The large tributary stream, Sycamore Creek, which has been excluded from this survey, adds an additional area of 117 square miles to the drainage area of the Red Cedar River. Three artificial impoundments are located.along the main course of the river. The Williamston dam was constructed in lBhO and at present maintains a 13 foot working-head of water. The Ckemos imp poundment is of the stone ballast type and creates a pool for recre- ational purposes. The East lensing impoundment is maintained on the campus of Michigan State University and is used for power plant supply. The river has its source at the outflOW'of Cedar Lake at an elevation of 93h feet above sea level. It falls to 817 feet at the confluence with the Grand River. The relatively gradual gradient is an average of 2.5 feet per mile. The bottom types are variable, with sand substrates being pre- dominant in the upper reaches. The lower portions are characterized by gravel and rock bottoms. The depth of the river rarely exceeds six feet in pools and is normally between two and three feet for long stretches below riffle areas. Seasonal depths vary according to the amount of precipitation. The minimum discarge recorded by the United States Geological Survey during a Zanear period from 1931 to 1951 occurred on July 31, 1931 when a flow of 3 cubic feet per second was measured. During the same period, the maximum.flow occurred during April, 19b6, when a flow of 5,510 cubic feet was measured. . Brehmer(l956) has characterized the river chemically. The Red Cedar River is a.warmewater stream which is slightly alkaline with a prof the water ranging between 7.2 and 7.8. The water is highly buffered, with the methyl orange alkalinity varying from 100 to 300 p.p.m. Dissolved oxygen determinations, at locations in the Williame ston area, revealed that the oxygen content of the water midway between the surface and bottom ranged above 90 percent of saturation. DESCRIPTION OF STATIONS A series of sites or stations along the Red Cedar River are herein described. The designated stations are arranged in an order from west to east, or from the lower course of the river at East - Lansing to the headwaters. Stations were selected for sampling in areas which were readily accessible by road. Most of the sites in- clude areas of considerable extent so that a variable number of ecological situations are embraced at each station. Although each h station is not a "type site" representing a characteristic ecological condition, the description of the area will give a graphic picture of the range of ecological conditions presently found in the river. Station I. Below East Lansing in the area downstream from Kala- mazoo Bridge, Ingham County, October 3, 1958. Mbre than one quarter mile of the river was searched, but no living specimens of naiads were found. The area sampled.was one half mile downstream from the sewage effluent of the City of East lensing and'Michigan State Uni- versity. The bottom type of the river was typically a coarse gravel. The depth was irregular, ranging between six inches and three feet. Station II. Michigan State University Campus, above sewage effluent, October 6, 1958. The specimens taken here were found in ten inches of water and in a coarse gravel substrate about twenty yards upstream.from the sewage effluent. Station III; Michigan State University Campus, at Beal Garden, October 9, 1958. The sample area was'in midstream at a depth of eight inches. The substrate was coarse gravel and some exposed rocks. Station N. Michigan State University Campus, below riffles and impoundment, September 28, 1958. A considerable current was found at this station. The sample area embraced two slightly differ- ent conditions. The first of these was the midstream.shallows with a coarse gravel substrate; the depth was approximately ten inches. The second was the deeper area close to the south bank. Here there .ere large rocks and pieces of exposed concrete. The depth exceeded two feet. Of the eight species found at this station, Fusconaia £l£33_occurred.mainly in the shallows. Station V. One half mile east of Michigan State University Campus, at the Sanford Wbodlot, September 25, 1958. The collection site was along the north bank of the river in the shallow water. The substrate was sand.under1aid by clay. Station VI. At Okemos, Ingham County, September 27, 1958. The river broadened after passing over a slight riffle. The bottom type was sand. Here the river was about two feet deep. Hummocks of aqua- tic vegetation provided a habitat for a number of different Species. Specimens were not found in the riffle nor in the shifting sand bars further downstream. Station VII. One and one half miles southeast of Okemos, Ingham County, October 3, 1958. TWO distinctive habitats were to be found here. A.midstream.area had a depth never exceeding three feet. The bottom was a rough gravel and sand substrate. A second habitat was the soft muddy banks on either side of the river. The depth here was variable and dependent on the slope of the river bed. Station VIII. TWO miles east of Okemos, Ingham.County, October 10, 1958. This station embraced a number of different substrates. A shallow gravel bottomed area, rich in detritus, yielded a variety of species. The single specimen of Alasmidonta calceolus was collected here. A coarse gravel and rocky substrate characterized another habitat at this station. The depth at the time of collection did not exceed three feet. A third area was a sand bar beneath a riffle at a depth of eighteen or more inches. This station was the richest in number of Species. Station IX. Three miles southeast of Okemos, Ingham County, October 10, 1958. Specimens were taken at either side of the Van Atta Road Bridge, which crossed the river at this site. Upstream the river passed over a riffle, below which a wide bottom area of sand was located. The depth below the riffle never exceeded three feet. Below the bridge the river narrowed and the depth increased at some points to over four feet. The bottom was a gravel which was rich in detritus. Further downstream the river becomes wider and the substrate becomes a mixture of sand and gravel. This station was quite rich in number Species but poor in total number of individuals per Species. Station X. Fbur miles east of Okemos, October 17, 1958. The river was crossed at this point by United States Highway 16. Im- mediatcly below the bridge was a small riffle. The depth ranged be- tween six inches and two feet. Downstream.of the riffle the current was strong. The bottom was mostly sand with a small amount of detri- tus. Upstream the bottom type of the river was changed, the sub- strate being predominantly gravel. The depth was constantly three feet. Station XI. One and one half miles northwest of Hilliamston, Ingham county, October 17, 1958. At this point the Zimmer Road Bridge crossed the river. The depth at this station ranged between eighteen inches and.two feet, with some depressionswhich exceeded three feet. The bottom type was gravel, but a great deal of silt had collected in some areas, notably in the depressions. This station was rich in numbers of species and seemed to be one of the best biologically productive areas in the river. The size of a number of specimens was impressive and indicative of the suitability of the habitat. Station XII. Below Williamston, October 17, 1958. This site was considerably below the impoundment and was close to the outer limits of the city. The river coursed through a well shaded hollow and assumed a constant width of thirty feet. The bottom was pre- dominantly sand and was rich in detritus. The depth of the river did not exceed two feet. Station XIII. Two and one half miles east of Williamston, Ing- ham County, October 2h, 1958. A large area of the river was searched on either side of the Deitz Road Bridge which crossed here. A num- ber of available habitats was present. Many sand bars, areas of deeper water with gravel substrate, and soft muddy banks were evi- dent, but the molluscan fauna was definitely impoverished. Station XIV. Three miles east of Williamston, Ingham.County, October 2h, 1958. Sites on both sides of the Michigan Highway h6 were sampled. The river assumed the width of a large creek and was, in some areas, approximately ten feet wide. The bottom type was sand, rich in detritus. A slight riffle was found. Some pools were three feet deep. Specimens were found imbedded in the sand at the roots of the stumps of trees within the slight riffle. Station XV. One and one half miles northwest of webberville, Ingham County, Nbvember 7, 1958. Only a single living specimen was taken here. The river assumed a constant width of about twenty feet and a depth of three to three and one half feet. A gentle bluff paralleled the river on the south while the northern bank was marshy. The bottom type was gravel. Station XVI. One and one half miles northeast of webberville, Ingham County, Nevember 7, 1958. samples were taken upstream from the Cranmer Road Bridge. No living naiads were found here. The bottom type was gravel and the river maintained a depth of not more than 8 two feet. A deep pool, probably manamade, was evident but the mollus- can fauna was lacking. Station XVII. Four miles southwest of Fbwlerville, Livingston County, Nbvember 7, 1958. At this site the Nest Branch of the Cedar River assumed creek-like proportions. The width of the stream was approximately ten feet from bank to bank. Midstream.depths were eighteen inches in.most places. The bottom was a mixture of gravel and sand, and the banks were clay. Most of the Specimens were found imbedded in the soft clay along the banks. A small Spring entered the river here. Air temperature was 1000, the Spring was 8°C, and the river was 6%00. Station XVIII. One mile south of Fowlerville, Livingston County, November 21, 1958. Here the Cedar River was approximately fifteen feet wide. The depth.was constant and did not exceed three feet. The river had been channeled and straightened for the purpose of agricultural. land reclamation. Considerable siltation had occurred. The banks were soft and muddy while the midstream bottom.was sand and gravel. In addition to the aforementioned stations a number of other sites were sampled where no naiads were found. At one mile intervals north- west of Fbwlerville, three sites were sampled. At Fowlerville, areas below and immediately upstream of a chemical effluent were searched. A few half-shells were found in the vicinity immediately upstream, but there were no evidences of naiad fauna below this site. Sampling on the Cedar River and the Middle Branch of the Cedar River yielded no specimens, except those collected at Station XVIII. The Cedar River was extremely soft-bottomed in those areas south of Fowlerville leading to its headwaters at the outflow of Cedar Lake. Marshy areas and flood.plains parallel the river through this section of its drain- age. Though representative naiads may be found, none were collected from this area during the present study. 10 u ‘ :7: 7|)! V c’LUTIQIm . ‘ .. ant-‘30.” aa<\ n (clams)... 1.... I’ l. >+c>ov . E £¢CH . — av \ _ e... 21.2.. .v. 7'“ . fl. _ .-— “54‘ :o. b S. h a 5*.E‘Q‘P-3 ’ ‘ 1" U n... U p 3:30 m5 BREW oz HFOMAAOO H852 60¢ fl hH .\ ‘r 1‘5 was/.3 flaw KEY FOR IDENTIFICATION OF THE NAIADS(UNIONIDAE) OF THE RED CEDAR RIVER 1. Surface of shell without postero-dorsal flutings.................2 Surface of shell with flutings or undulations confined to postero- dorsal margin;shell laterally compressed.......Lasmigona costata 2. Hinge with well-deveIOped pseudocardinal and lateral teeth.....3 . Hinge with laterals or pseudocardinals or both missing.........9 3. Epidermis black or brown, rayless when adult;faintly rayed when younEOOOOOO0.0..0...OOOOOOOCOOOOCOOOOOOOOOOOOOOOOOOOOOOOOOCOOOCO Epidermis yellowish, greenish smooth or polished with.more or less distinct rays;rarely yellowish and rayless.................6 h. Nacre usually white, height of shell 70% or more of length.....S Nacre usually violet or purple, height of shell 60% or less Of lengthOOeeeee00000000000000.eeeeeeeeeeeeemligtio dilatatus 5. Posterior ridge angles with slight depression or sulcus in front; umbonal sculpture subconcentric bars.............Fusconaia flava Posterior ridge not angled, evenly rounded, no distIEEt—EEIcus or depression3umbonal sculpture nodulose........................ ...................................Pleurobema cordatum coccineum 6. Shell solid, thick;hinge with large triangular pseudocardinal teethgfidth more than 30% Of lengthwnuo....................7 Shell thin to fragile3hinge weak;pseudocardinal teeth reduced to remnant;width 1683 than 30% of length..........Micromya iris 7. Beak sculpture of fine wavy concentric lines;epidermis dark green to yellowish green with dark green rays more or less distinct; shell small.............................Actinonaias ellipsifomis Beak sculpture of strong double-100ped ridges or with coarse non- wavy lines;epidermis yellowish green or reddish, rays well developed, or feeble, rarely absent.............................8 8. Height less than 65% of length;umbones not greatly inflated; beak sculpture of 6-10 double-looped bars.Lampsilis siliquoidea Height more than 65% of length;umbones inflated above—the hinge line;beaksculpture of h-S coarse non-wavy lines................. oeeoeeeeeeeeeeeeeeeeeeeeeeeeeeeOeeeeeOOOOOQIIaUPSili3 ventricosa 9. Hinge completely edentulousuuu"nun...o......u.........".10 Hingc nOt completely CdentulmlSOOeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeu lO. Beak markings distinctly double-looped..........Anodonta grandis Beak markings consisting of subcentric bars more or Iess diagonal to the hinge lino...................Anodontoides ferussacianus 11. Pseudocardinal teeth absent or reduced...........................12 Pseudocardinal teeth present and well developed..................13 12 12. Hinge with well-developed(though slight) lateral teeth, but with pseudocardinals reduced to mere tubercles...Lasmigona compressa Pfinge line thickened;pseudocardinals representedfby small tuber- cular thickening.............................Strophitus rugosus 13. Shell less than 50 mm.in length;posterior ridge more or less romadOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOAlasmj-donta calCOOIuE Shell more than 50 mm in length;posterior ridgeihigh and well developed..................................Alasmidonta marginata 13 >4 >4 ma :50.“ “25:0 nauauoflflwwfl smouunpaoe eaanmaswn .3399 SH» 3 Season N of: seasons“: seesaw.” me canoe «Sea 3 mméoooaso 3:028»on x msmommwu 303a?“ pm Mono “commune.“ no“ 30:035. >4 >4 >4 >4 >4 >4 >4 >4 >4 ' >4 >4 >< >4 x N «9339 snow anon N $399800 snow «Emma >4 >4 >4 >4 >4 >4 >4 .25on 3335 gonwoooo .Eoo espoused“ >4 >4 )4 >4 >4 >4 >4 x N x N dead :28er N x assassin 333E imamadoammammsmma «$522058 mmbwm ~30me film mg... as mzpbbwtm Opphromflwco E mm??? .wC 2c FQmEmHQ Ewe H Egg. DISCUSSIOV OF SPECIES ELLIPTIO DILATATUS (RAFINESQUE) This Species was the most abundant form in the river. The dis- tribution was widespread, for it was found at nearly all stations in the main course of the river. Although this form occurs in large rivers and also in large creeks, it is predominantly a small-river species. Its relative abundance was indicative of the small-medium river conditions which charaterized the Red Cedar. This species, as are all other naiads, was absent below the outfall of the sewage plant below East Lansing. Ecologically, E. dilatatus was most often found in a substrate of sand. Some large specimens were taken in a substrate of heavy angular gravel, often around the bases of rocks or pieces of concrete that were eXposed. At Station VI this species was most abundant and was found burrowed in the sand at and around the roots of aquatic plants. However, a large representation of this species was also found at Station XI where the river was heavily silted and highly productive. Some Specimens from the station were diseased, and a number of tiny pearls were discovered in their mantles. A single specimen at Station V was found in sand.under1aid by clay. Van der Schalie (1938:h8) has shown the types of bottom from which the Species has been obtained and adds: "The fundamental re- quirement is not so much a matter of the kind of substratum as it is of its firmness. It can and does do well on practically all types of bottom with the exception of muck, which is too soft, and clay, 15 which is too hard." With few exceptions the epidermis of all the specimens taken from the river are intact. Since beak erosion is common in many streams, it is obvious that the causal factors are chemical, for one might expect to find the beaks of a species living in sand and gravel to be eroded. This Species is variable in form and color. Its wide distri- bution in a number of different habitats indicates its vagility. Young shells have a rounded ventral margin while older shells are ventrally arcuate. Immature specimens may be distinctly rayed. The nacre is most often dark purple, but a veritable myriad of colors may be encountered, which range from white, to pink, to blue, and to purple. It has been contended(0rtmann, 1920) that the nacre of this species becomes whiter in specimens downstream from the headwaters to the mouth and that older Specimens tend to fade to a pearl blue or whitish ground color. No tendency is evident in my specimens, but rather it was found that the shells varied from individual to indivi- dual. At stations where Eh dilatatus were abundant, one might en~ counter the full gamut of variability in nacreous color. It must noted that the rchr yielded no specimens from.below East Lansing, and that, consequently, there may not have been enough material to make a thorough representative sample. FUSCOBIAIA FLAVA (RAFIPIE‘SQUE) During this study this Species was well distributed along the main course of the river. It was considered common since the number of specimens collected indicate that it was next numerous in abun- 16 dance to Elliptig dilatatus. Although this Species is typically found in small or medium river conditions, its distribution is not necessar- ily restricted to these localities. A single Specimen was taken at Station XVII where conditions were typically those of a creek, and dead specimens were collected above Fbwlerville where the river had become appreciably smaller. In the Red Cedar this species was found mostly in a substrate of sand, in which it was typically burrowed; however, a gravel substrate was the preferred bottom type at a number of sites. At Station IV where E, flgzg was locally abundant, the Specimens were found in.the shallow midstream area on a bottom of rough gravel. At Stations VII and VIII the Species was common in a similar habitat of shallow water and rough gravel.’ The silted areas of Station XI yielded many large Specimens, and the Species was locally abundant. The definitive characters of specific identification in forms similar to E, £laza_are based.upon the nature of the glochidial sacs. In Pleurobema cordatum coccineum (Conrad), a species easily confused with E, flava, only the outer gills serve as marsupia while in E. flava all four gills are marsupial in function. Since both forms are tachytictic and since this collection was made in the fall and early winter, no Specimens were in a gravid condition at the time of collection; therefore, only diagnostic shell features were used to differentiate the two forms. Although F. flava varies in size, shape, and nacreous color, its general features are characteristic enough to separate it from E, cordatum coccineum. A definite posterior ridge, with a more or less 17 distinct depression in front, a beak sculpture consisting of 3 to 5 subconcentric bars, and a beak cavity noticeably deeper than in E, cordatum.coccineum distinguish this Species. In E. cordatum 2227 cineum the beak cavity is shallow, the posterior ridge is reduced to a rounded swelling and is often totally wanting, and the teak scul- pture is irregularly nodulose. The pseudocardinal teeth are more massive, less elevated and lack the sharp serrations of the more acutely pyramidal pseudocardinals of’g} flava. Several Suthors use the placement and directional slope of the lateral teeth, a character which seems too equivocal in regard to the variation of size and shape of the shell. The outline or Shell shape of E. £1313 tends to be elongate-quadrate or trapezoidal while the shape of E. cordatum coccineum is typically subtriangular with a tendency for the shell to attain a rounded appearance. PLEUROBEm CORDATU}? 1000 Drum: (octrtmn) This species was relatively uncommon in the Red Cedar River although in some localities it made up an appreciable part of the fauna. Its distribution was restricted to the main course of the river where it was sporadically represented. In the shallows of Stations IV, VII, and IX, the specimens were found burrowed in the gravel substrate. Fine large Specimens were found in the coarse gravel of the silted areas of Station XI. Although this Species has been found in shallow sand bars and on substrates of sand, it was not taken in this typical habitat in the Red Cedar. Van der Schalie (l9h0) has shown that this Species was not found east of Nilliamston. The present study corob rates this further and shows that P. cordatum -“ 18 v. gosaoooo Eustace «.5032:ch x «>03 «3:00um . .mo 20 Hebm 96m .8 N n22 19 2 /\ mapmaaaac oaeaaaaw. mo onSmHEm B was 20 coccineum has hardly changed its geographical and ecological posi- tion in the fauna of the Red Cedar River. The shell characters and their value in specific determination are discussed with Fusconaia flava, a Species with which E. cordatum coccineum is most often confused. ANODONTA GRANDIS SAY The distribution of this Species was as widespread as any in the river. It was found throughout the main course of the river and in both tributaries, the Cedar River and the Riddle Branch of the Cedar River. This species has a variable range of habitats but is often found in bottom types that are soft and in areas where current is not too strong. At Station VII many Specimens were found along the banks imbedded in the muddy bottom, rich in detritus and fallen leaves. The water was remarkably clear and the Specimens could be easily seen in the shallow water. At this station the Species was most abundant and outnumbered any other forms. At Stations VIII, IX, and XI, some Specimens were taken on gravel and sand bottoms. At Station XVII it was found along the banks but imbedded in clay. fiith its thin shell, this Species is especially adapted for living on a soft bottom in more or less quiet waters and can exist in some muddy areas where few other forms can survive. Anodonta grandis has a variable shell throughout the Red Cedar drainage, as it has elsewhere in its range. Descriptions of the varietal forms have been made, but the intergradation of these forms mades an adoption of specific, or in some cases subSpecific, names untenable. Since the Species is often found in ecological conditions 21 that may bring about a variation, one is Iorced to conclude that ecological races constitute differences appearing in the shells. One such form is found with a characteristic nacre that is salmon- colored and often blistered. This is a pathologic condition brought about by the presence of a parasitic worm. LASICIGONA COE-ZPZZESSA (LEA) This Species is typical of creeks and small streams and extends far into the headwaters of rinrS(Baker,l928). It was found alive at only two stations and was one of the naiads of the Red Cedar that may be considered rare. Beauchamp(1883) observed that the Species preferred small streams with muddy bottoms and that there it often formed isolated colonies. Baker(l928) typified its habitat as fine gravel, sand, or mud. In the Red Cedar River the Species was never taken in association with a muddy bottom. At Station XIV it was found in a Sand substrate, below a slight riffle in a small pool or depres- sion approximately three feet deep. At Station XVII it was collected in the west Branch of the Cedar River, which assumed the proportions of a creek. Here the specimens were imbedded in the clay along the bank. Unfortunately, only a few specimens of this species were col- lected , but it was found that the distribution of this Species was limited to the hradwaters of the river and to areas of the river which were typically creek-like. ‘E. compressa was confined to the upper reaches of the drainage and E. costata to the main course and lower portion of the Red Cedar River. The shell caracters of I? cogpressa ar as distinct as its characteristic ecology. The shell itself is marked with broad, grass- 22 green rays, and is typically compressed. Little variasion occurs in the shell or nacre of this species. LASHIGOHA COSTATA (RAFINESQUE) The Species was well distributed along the main course of the river, but did not extend into the upper reaches of the tributaries, and was not found East of Williamston. van der Schalie(19h0) found this Species rather sparsely represented in_the Red Cedar fauna. This study showed that the species was quite common, although never abundant. It was found most often in a gravel substrate. At Stations VI and X, it was collected.below the riffles in sand and gravel where the current was strong. Below the riffles at Station IV the Species was discovered wedged in gravel at the base of larger rocks or pieces of concrete that were exposed. At Station XI some very large Speci- mens were taken in the typical gravel substrate but in areas that were heavily silted. The shell may be readily distinguished by the rugose posterior margin and peculiar hinge structure. There is not a great deal of variation in the species. The complexity of the flutings on the posterior wing may vary. Some specimens show the posterior rugo- sities more strongly while in others they are less developed. The color is also variable, from greenish to yellowish-brown, the young shell being usually beautifully rayed. Older shells tend to be quite dark brown. ANODONTOIDES FERUSSACIANIIS (LEA) This species was quite uncommon in the Red Cedar River and 23 occurred rarely west of Okemos where the river b-came deeper and larger. It is a creek form and occurs most often in pools with a sand or gravel substrate(Baker,l928). .t Stations VII, VIII, and XII it was found in a substrate of gravel and sand. Station XIV was a typical habitat for this Species, although it did not occur abun— dantly. The distribution of this Species extended into the west Branch of the Cedar River, where Specimens were found under creek- like conditions along the banks inbedded in clay. No specimens were taken at Station XI, which, although rich in number