14 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 487 



species in the two bogs (fig. 3) seems to have no correlation with the depth of 

 the sample. The shell is elongate -cylindrical and may vary in length from 20 

 to 30 mm. However, the few shells collected in these deposits are either im- 

 mature or broken, and are much smaller than the typical dimensions. L. lanoeata 

 has been reported from southern Ontario to Ohio and Wisconsin. 



L. lanoeata, sparsely and erratically distributed in the Strawn and 

 Batavia bogs, certainly cannot be considered a significant element of the faunal 

 assemblages . 



Lymnaea {Stagnioola) palustris (Miiller) 1774 



Bucoinum palustre Miiller 1774, Verm. Terr, et Fluv. Hist., p. 131. 

 Stagnioola palustris (Miiller), La Rocque 1968, Ohio Div. Geol. Surv. 

 Bull. 62, pt. 3, p. 443, fig. 294. 



A single shell of L. palustris was taken from the uppermost sample at 

 locality 135-2 (fig. 3). The species is one adapted for living in a small lake 

 habitat, but the single shell makes it doubtful that established populations 

 inhabited the lake at the Strawn locality. L. palustris has an elongate spiral 

 shell usually more than 20 mm high. 



Lymnaea {Fossaria) dalli F. C. Baker 1906 



Lymnaea dalli F. C. Baker 1906, Illinois Lab. Nat. Hist. Bull., v. 7, 

 p. 104. 



Fossaria dalli (F. C. Baker), F. C. Baker 1928, Freshwater Moll . 

 Wisconsin, pt. 1, p. 288, pi. 16, fig. 11. 



L. dalli is a tiny gastropod with a typical lymnaeid shell no more than 

 about 4 mm in length. The living species occurs more often near water than in 

 it, on mud and debris near the water's edge. It is widely distributed in North 

 America, probably more so than records indicate because its small size leads 

 to its being overlooked. It occurs in five of the faunal assemblages (fig. 3), 

 in fair numbers in some collections. In spite of this fact, it is doubtful that 

 the animals lived where the shells were found, because L. dalli is rarely if 

 ever found far from shoreline habitats. 



Lymnaea {Fossaria) obrussa Say 1825 



Lymneus obrussus Say 1825, Acad. Nat. Sci. Philadelphia Jour., v. 5, 

 p. 123. 



Fossaria obrussa (Say), F. C. Baker 1928, Freshwater Moll . Wisconsin, 

 pt. 1, p. 239, pi. 18, figs. 14-24. 



L. obrussa is a rather small lymnaeid gastropod, the shells varying from 

 9 to 11 mm in length; it is larger than L. parva and the ultimate whorl is more 

 swollen than it is in L. parva. L. obrussa was not recovered from any level at 

 locality 135-1. It occurs sparingly in three faunal assemblages at locality 

 135-2, but is found at every level among the samples from locality 136 (fig. 3) . 

 Even at the Batavia bog (136) L. obrussa does not occur in abundant numbers, 

 although its regular occurrence would indicate it as a part of the indigenous 

 molluscan population. 



Lymnaea {Fossaria) parva Lea 1841 



Lymnaea parva Lea 1841, Amer. Philos . Soc. Proc, v. 2, p. 33. 



