1883.] NATURAL SCIENCES OF PHILADELPHIA. Itl 



DESCRIPTION OF A NEW HYDSOBIINOID GASTEEOPOD FROM THE MOUN- 

 TAIN LAKES OF THE SIERRA NEVADA, WITH REMARKS ON ALLIED 

 SPECIES AND THE PHYSIOGRAPHICAL FEATURES OF SAID REGION 



BY ROBERT E. C. STEARNS. 



The interesting form herein described was first brought to m}' 

 notice through the kindness of Mr. Xenos Clark, son of the 

 lamented Prof. Henry James Clark, in 18V9. Owing to ill-health 

 and other causes, it has remained nndescribed until this time. 

 Recently I have been stimulated to inquire into its characters and 

 relationship, by the reception of a letter and further specimens 

 from Prof. R. Ellsworth Call, who, while believing it to be nnde- 

 scribed, thought possibly it had been made known by some of our 

 West Coast naturalists, and wrote to me for information. 



While it appears to have certain analogies with Lioplax of the 

 Viviparidffi on the one side (see L. suhcarinatu Sa}'), and witli 

 the Strepomatidai (see the carinatcd Goniobases like G. torulosa ^ 

 Anthony), on the other, yet the sum of its characters, inclusive 

 of faunal and geographical relationship, seems to me to point 

 rather in the direction of the fresh-water Rissoids. The late Dr. 

 Stimpson's genus Tryonia applies only to shells with a " surface 

 longitudinally ribbed or plicated,*' as distinct from the usual 

 smooth-surfaced shells of the various groups embraced in his 

 '•Researches, etc."'^ He includes, however, the little group 

 Pyrgula of Cristoforo and Jan, and arranges it directly preceding 

 Tryonia, which my judgment confirms as being its proper place. 



Woodward ^ included this genus (Pyrgula) in his syuon3-my of 

 Melania ; he also placed Amnicola as a subgenus of the foregoino-. 

 H. and A. Adams * place Pyrgula with the Melaniaus, but Amni- 

 cola Ts grouped by them with the Rissoidne. The}- further include 



' L. and F. W. Shells of N. A. Part IV, p. 229, S. T. Miss. Coll., 258. 

 See also Meek and Hayden's Tertiary Goniohans temiicarinata, Proc. 

 Phila. Acad. Nat. Sci., 1857, p. 124, and G. nebrascensis, id., 185G, p. 124. 

 Also Wheeler's Report. Palgeoiitology, vol. iv, and Hayden's Inv. Palagou- 

 tology, vol. is. 



* Researches upon the Hydrobiinae and allied forms. Smitlis'n Misc. 

 Coll., 201. 



■^ Recent and Fossil Shells, 2d ed., pp. 246, 247. 

 ^ Adams' Genera, pp. 305-308, vol. i. 



