32 NEW YORK STATE MUSEUM 



ference between the American and the European forms, described 

 the form asPleurot o mari a a in e r i c a n a . As Ulrich has 

 pointed out lately, some other of Billings's species have been cur- 

 rently referred to P 1 e u r o t o m a r i a lenticularis, viz 

 P. vitruvia and P.progne. Both of these, when only casts 

 are at hand and the surface characters are obliterated, can still 

 be distinguished from the large Liospira americana, 

 as the game investigators have demonstrated, by the character 

 of the umbilicus, Liospira vitruvia and americana 

 having an open umbilicus, while that of Liospira progne 

 is closed. Liospira vitruvia and americana can be 

 distinguished in sections by the angular margins of the umbilicus 

 and its flattened side® in the former; the margins and sides of 

 Liospira americana being round. A drawing of a sec- 

 tion of the Liospira found in the Rysedorph hill comglomerate 

 has been given; it shows that by the character of its umbil- 

 icus it can be referred only to L i o> s p i r a americana. 



Mr Ulrich has separated such species 1 as PLeurotonuaria 

 americana, which are distinguished by their sublenticular 

 shell, low depressed spire, almost smooth surface and subrhom- 

 boidal volutions, as Liospira The section figured shows dis- 

 tinctly the subrhomboidal section of the volutions as well 

 as the depressed conic form of the shell. The Paleontology of 

 New York, v. 1, reports this species from various Trenton localities, 

 stating that it is most common in the higher crystalline por- 

 tions of the rock at Watertown. Dr White cites it also from 

 the Black river beds at Rathbone and West Canada creeks, and 

 Prosser and Cumings 1 also found a form, doubtfully referred to 

 this species, in the Black river beds near Newport. In Canada, 

 Tennessee and the Cincinnati region, it has, however, been found 

 in beds corirespoinding in age to the Lowville limestone. Its geo- 

 graphic distribution is great, for it has been found at Silliman's 

 Fossil Mount in Baffin Land, is reported by Dr Whiteaves 2 from 

 the Trenton beds of Lake Winnipeg and occurs in Minnesota and 

 Tennessee. 



i N. Y. state geol. 15th an. rep't 1898. 1 :631. 

 a Pal. fossils. 1897. v. 3, pt 3, p. 191. 



