10 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 487 



Sphaerium simile (Say) 1816 



Cyolas similis Say 1816, Nicholson's Encyc . , v. 2, pi. 1, fig. 9. 

 Sphaerium simile (Say), Burch 1972, Biota Freshwater Ecosystems, 

 Washington, p. 6, 10, fig. 5b. 



The specific name of this common sphaeriid mussel has long been a 

 matter of controversy; the problem was discussed in some detail by F. C. Baker 

 (1928, p. 316). Herrington considered the problem and indicated that simile 

 is not a synonym of sulcatum. However, Burch (1972), who worked with Herring- 

 ton, does not recognize sulcatum, but uses Herrington' s figure of sulcatum to 

 illustrate simile. Since the species is widely distributed in North America, it 

 probably is a native element of the sphaeriid complex, distinct from sulcatum. 



The large shell of S. simile occurs in 12 of the 27 faunal assemblages 

 considered (fig. 3), but in none are the valves numerous. They vary from frag- 

 ments to eight complete valves. At localities 135-1 and 135-2, simile does 

 not occur in the uppermost 5 to 6 feet of the deposits, but at the Batavia locality, 

 136, simile ranges throughout the section. 



Sphaerium fabale (Prime) 1851 



Cyclas fabalis Prime 1851, Boston Soc. Nat. Hist. Proc . , v. 4, p. 159. 

 Sphaerium fabale (Prime), Herrington 1962, Revision Sphaeriidae 

 N. America, p. 18, pi. 2, fig. 3. 



A single valve recovered from the 12-foot level of locality 136 is the 

 only evidence of this species in the bogs under study. It seems unlikely that 

 the animal lived in the lake itself, at least where the auger boring was made. 

 This valve is somewhat smaller than those described by Herrington, but it seems 

 to be a mature shell. 



S. fabale is distributed in North America from Vermont to the Mississippi 

 River; it has been reported in Canada from southern Ontario. 



Genus Pisidium Pfeiffer 1821 



The shells of the genus Pisidium are small, rounded or ovoid to cuneiform . 

 seldom much over 6 mm in length. They differ frorn those of Sphaerium inasmuch 

 as the beaks are posterior. The species recognized in North America are divided 

 arbitrarily into two groups: four "large" species and 21 "small" species. The 

 two species of Pisidium considered here belong to the "small" group. 



Pisidium compressum Prime 1851 



Pisidium compressum Prime 1851, Boston Soc. Nat. Hist. Proc, v. 4, 

 p. 164. 



Pisidium compressum Prime, Herrington 1962, Revision Sphaeriidae 

 N. America, p. 35, pi. 5, fig. 2; pi. 7, fig. 14. 



The shell of P. compressum is 3.5 to 4.0 mm long, robust for its size, 

 and characteristically trianguloid in shape. In our collections, it occurs in 21 

 of the 27 faunal assemblages and is numerous in every occurrence; it is absent 

 from the uppermost 4 to 6 feet of the auger samples at localities 135-1 and 

 135-2, but occurs abundantly throughout the several levels of locality 136 

 (fig. 3) . A few united pairs of valves were observed at each of the localities 

 studied. 



