146 



I^'^D AND FRESH WATER SHELLS OF X. A. [PART IL 



Ancylns fragilis, Tryox. — Shell very small and fragile, sides 

 nearly parallel or slightly incurved in the middle, but diverging anteri- 

 orly ; ends rounded. Apex elevated, acute, curved backwards, with about 

 two-thirds of the shell anterior to it. Size of the largest speci- 

 men : Length 4, breadth 1.15, height 1 mill. Most of the 

 specimens do not exceed two-thirds of the dimensions. 



Laguna Honha, California : Rev. J. Rowell. My cabinet, 

 and cabinet of Mr. Rowell. 



This species is smaller, thinner, and wants the convex lateral 

 margins of our Anc. rivularis, Say. It agrees with that shell, however, in 

 the greater width of its anterior end, while in the shape of its lateral 

 margins it resembles Anc, parallelus, Hald. It is much the smallest of our 

 species. {Tryon.) 



Ancylus fragilis, Tryox, Proc. Phila. Acad. Nat. Sc. 1863, 149, pi. i, f. 15. 



Mr. Tryon's description and figure are copied above. 



Fig. 246. 

 <^ 



Aneylus 

 frogiUs 



Fig. 247. 



Doubtful Species of Ancylus. 



Aneylus drouetianus, Bourguignat. — Shell slightly convex anteriorly, 

 straight posteriorly; summit small, sharp, contracted on its sides, 

 recurved and resting on the posterior wall of the shell, a support 

 which does not always secure it from fracture. Apical de- 

 pression invisible on account of the apex being bent backwards. 

 Shell very smooth, shining, transparent and horn-colored ; surface 

 divided into fifteen triangular compartments, 

 commencing at tlie apex and enlarging to- 

 wards the base of the shell, the dividing ridge 

 marking the peristome in an undulating 

 manner. Length 6, height 2-2], breadth 5 

 mill. 



Habitat unknown, but from its character- 

 istics probably belonging to North America. 

 Dedicated to my friend Henry Drouet of 

 Troyes. 

 Belonging to the group of A. crassiis, radialllU, rivttlaris, &c., but easily 

 distinguished by its triangular divisions and undulating peritreme. 

 Its apex and mode of growth also distinguish it from A. riparins 

 and ritraceus, which share its other characteristics just mentioned, 

 though they have a very apparent apical depression. {Bounjuignnt.) 

 The above description and figure are copied from Bourguignat's Memoir 

 on Aiiciilus (Proc. Zool Soc. 1S53, p. 92, pi. xxv, f. 10-17). 



Having never seen or heard of any such species in the United States, I 

 .Iduht its existem-e there, but have given the description and figure to 

 facilitate its recognition should it be found. 

 Aneylus Jilosus is an Acroluxus. 



Anoylus drouetianus. 



