HANNIBAL: CALIFORNIAN FRESRWATER MOLLUSCA. 189 



P. Nevadensis is the only living representative of the genus west 

 of the Rocky Mountains. To this must be added, however, several 

 additional forms particularly from the Pliocene lake deposits of 

 California. Other undescribed Amnicolids from the extensive 

 lacustrine beds of this period on the coast are probably conseneric, 

 but the writer prefers to delay their description until the sculptured 

 forms are discovered and their generic position positively established. 

 The Pyrgulopses are characteristically localized in distribution, and 

 the fossil forms were apparently rather short-lived, hence become 

 valuable in horizon determination. 



Pyrgulopsis antiqua (Gabb). 

 Lithasia antiqua, Gabb, 1866. 



Shell large, sub-globose, spire elevated, whorls rounded and smooth, 

 sutures somewliat impressed, aperture ovate, outer lip slightly sinuate, 

 peritreme incomplete ; habitat apparently lacustrine. 



Eocene : Payette Lake beds, Idaho and Oregon. 



The writer has seen specimens of this species, but has not had the 

 opportunity to study the early whorls. While the large size and 

 globose form suggest Anculosa somewhat, there is scarcely any 

 likelihood that it belongs to that family. Its affinities are rather 

 with the present group, though it is by no means certain that it is 

 really congeneric with P. Nevadensis. The proper disposition of 

 fossil Amiiicolidge into their respective genera is fre(iuently rather 

 embarrassing owing to the absence of well-marked shell characters. 



Pyrgulopsis Nevadensis (Steai'ns). 

 Pyrgula Nevadensis, Stearns, 1883. 



Shell of moderate size, slender- conic, imperforate, spire decidedly 

 elevated, sutures well impressed ; habitat lakes. 



Nevada System (locally). 



Quaternary : Lahontan Lake beds, Nevada. 



The prevailing form is peripherally carinate. 



Pyrg0lopsis Yatesiana (J. G. Cooper). 

 Anmicola Yatesiana, J. G. Cooper, 1894. 



Shell rather large, pupiforra-globose, umbilicate, spire somewhat 

 elevated, sutures not deeply impressed ; habitat, apparently a lake 

 species. 



Pliocene : Santa Clara Lake beds, California. 



The prevailing form is the rounded one, but peripherally carinate 

 individuals are not rare at certain localities. 



Pyrgulopsis Williamsi, n.sp. PL VIII, Fig. 29. 



Amnicola ' turhiniformis, Tryon ', J. G. Cooper, 1894. 



Shell of very large size, broadlv conic-globose, sub-jierforate, spire 

 somewhat elevated, sutures more or less impressed ; habitat, apparently 

 a lake species. 



