70 LAND AND FRESH- WATER SHELLS OF N. A. [PART III. 



Pomatiopsis biniieyi, Tkyon, Proc. Pliila. Acad. 18G3, 148, pi. i, f. 10. 



Mr. Tryon's description is given above, as well as a fac-simile 

 of his figure (Fig. 136). I have also given another figure of his 

 original specimen. 



Bytliinella ol)tusa. Lea. — Shell subcylindrical, rather thin, dark- 

 green, smooth, slightly perforate ; spire short ; at the beaks very obtuse ; 

 sutures impressed ; whirls four, convex ; aperture small, nearly 

 round. 



Ohio. Diam. .07, length .10 inch. 



This is among the smallest of the genus, and may at once be 

 distinguished by its obtuse apex, which has the appearance 

 almost of being truncate. The whirls do not decrease regu- 

 larly from the lower one to the apex, the greatest diameter being 

 apparently across the second whirl. In form, therefore, it has 

 the aspect of a Pupa. It answers partly to the description of Paludina 

 allcghaniensis, Green, but seems to differ in the truncate appearance of the 

 apex, and in its size. Two specimens were found in a box, with some 

 other small species, kindly sent me by Dr. Kirtland. It is rather less 

 than Pal. nickliniana, but differs from it in being less tapering to the 

 apex. It closely resembles P. viridis, Lam., but is rather larger, and more 

 obtuse. There were no opercula to examine in these specimens ; apertuio 

 rather more than one-third the length of the shell. (Lea.) 



Paludina obtusa, Lea, Tr. Am. Phil. Soc. IX, 13 (1844) ; Obs. IV, 13 ; 



Proc. II, 34 (1841). 

 Amnicola obtusa, Haldeman, Mon. p. 24 (1844?). 



Figure 138 is drawn from Mr. Lea's original specimen. 



TRYOIVIA, Stimpson. 



Shell perforate, elongated, turreted, subulate, acute at summit 

 and rather pointed at baso ; surface longitudinally ribbed or 

 plicated, not spinous ; whirls numerous, shouldered. Aperture 

 small, oblique, rhombo-ovate ; and somewhat pointed, sinuated, 

 and effuse at base ; outer lip thin and sharp, projecting below ; 

 inner lip appressed to the whirl above, peritreme however con- 

 tinuous. Operculum and lingual dentition unknown. 



Station, fresh water. 



Distribution, Southern California. (Slimpson.) , 



