CALL AND PILSBRY ON PYRGULOPSIS. 



ON PYRGULOPSIS, A NEW GENUS OF RISSOID 



MOLLUSK, WITH DESCRIPTIONS OF 



TWO NEW FORMS. 



BY R. ELLSWORTH CALL AND HARRY A. PILSBRY. 

 It 4a J before the Academy, February 2bth, iSSb. 



In September, 1883, Mr. R. E. C. Stearns described a rissoid mol- 

 lusk from Pyramid Lake, Nevada, under the name of Pyrgula neva- 

 densis. His description was based, in part, upon material furnished 

 by one of the present writers, which was, at that time, inconsiderable 

 in amount. In the following year the form was collected in almost 

 incredible numbers in the original locality, and studied by Messrs. 

 Call and Beecher in as complete a manner as rather unfavorable cir- 

 cumstances would admit. At that time the generic reference of the 

 species appeared to be unquestionable, and, in the absence of speci- 

 mens of European Pyrgula for comparison, was agreed upon as prob- 

 ably correct. Since this later study of the Nevada form, in which the 

 dentition was illustrated and found to be rissoid, additional data have 

 accumulated, which appear to render impossible the original generic 

 reference. These data consist, in the main, of a careful study of the orig- 

 inal bibliographic matter concerning the institution of Pyrgula as a 

 genus, of the discovery of at least two additional forms which seem to be 

 congeneric with Pyrgula nevadensis, neither of which agree with typical 

 Pyrgula, either in station or understood hypsometric range, and of 

 certain conchologic features that appear in the following diagnosis. In 

 the further absence of any generic group which will include these shells, 

 it has seemed proper to institute for their reception a genus that would 

 do no violence to their conchologic affinities or to their geographic 

 distribution. We therefore propose the name of Pyrgulopsis for these 

 forms, and define the genus as follows: 



Pyrgulopsis, gen. nov. 



(Etymology: Pyrgula, ami opsis aspect of.) 



Type, Pyrgulopsis nevadensis Stearns. 



Pyrgula nevadensis Stearns.- Proc. Phila. Acad. Nat. Sci., 1883. 



Generic characters : Shell minute, conically turreted, somewhat 

 elongated, imperforate, unicarinate; apex acute; aperture ovate; peri- 

 treme continuous. 



TPkoc. D. A. N. S., Vol. V.J 2 [May 25, 1886.] 



