POST-WOODFORDIAN MOLLUSKS 13 



The shells of this species have a characteristic bulbous shape produced 

 by the large ultimate whorl, which differs little between the sexes. The shells 

 are spiral, turbinate, and relatively small, the height being no more than 5 mm 

 in adult specimens. Like A. gelida, A. leightoni is presumed to be an extinct 

 species, which has been reported from Pleistocene marl deposits in Illinois, 

 Ohio, Indiana, and elsewhere in nearby states. 



Amnioola leightoni occurs in every one of the 2 7 faunal assemblages 

 studied and forms abundant populations in each of them. It was one of the 

 earliest colonizers of these bogs, and occurs in the lowermost fossiliferous 

 samples at each locality. 



Subclass Euthyneura 

 Order Pulmonata 

 Suborder Basommatophora 

 Family Lymnaeidae 



Genus Lymnaea Lamarck 1799 



The lymnaeids are pulmonate aquatic gastropods, widely distributed over 

 the world, especially in the northern hemisphere. The animals are extremely 

 sensitive to local environmental conditions and to fluctuations in them, which 

 has led to great taxonomic confusion and needless proliferation of names. 

 Baker (1911) subdivided the genus Lymnaea into several genera; this subdivision 

 has been widely, although not universally, accepted. The lymnaeids seem 

 rather to be represented worldwide as a small number of highly variable species, 

 as pointed out and so ably defended by Hubendick (1951). 



In this work all taxa of lymnaeids are listed in the genus Lymnaea, as 

 seems proper, especially in the case of fossil shells, but the names of the 

 Bakerian genera are inserted as subgenera in order to reflect wide usage among 

 students of the family Lymnaeidae. 



Aquatic pulmonate gastropods possess no gills; they mediate gaseous 

 exchange through a pocket in the mantle, or through the general body surface. 

 Active lymnaeids have been found at great depths, indicating their independence 

 of free gaseous oxygen. 



Although several taxa of lymnaeids occur in the two bogs under investi- 

 gation, the shells are nowhere numerous and should be classed everywhere in 

 these bogs as rare. 



Lymnaea {Stagniaola) oaperata Say 1829 



Lymneus caperatus Say 1829, New Harmony Disseminator, v. 2, p. 230. 

 Stagniaola oaperata (Say), F. C. Baker 1928, Freshwater Moll. 

 Wisconsin, pt. 1, p. 260, pi. 18, figs. 43-47. 



L. oaperata is represented in these collections by a single example 

 (fig. 3), which was probably transported into the bog from small brooks that 

 flowed into it. It cannot be said to have recognizable significance in this study. 



Lymnaea {Stagnioola) lanoeata Gould 1848 



Limnaea lanoeata Gould 1848, Boston Soc. Nat. Hist. Proc, v. 3, p. 64, 

 Stagnioola lanoeata (Gould), F. C. Baker 1928, Freshwater Moll. 

 Wisconsin, pt. 1, p. 228, pi. 14, figs. 12-15. 



L. lanoeata occurs in only 6 of the 21 faunal assemblages, and in each 

 of these is represented by only one to three shells. The occurrence of the 



