1883.] NATURAL SCIENCES OF PHILADELPHIA. ITS 



they are distributed. At Walter's Station, on the Southern Pacific 

 Railroad, the perpendicular section exhibited by the digging of a 

 well to the depth of forty-seven feet, contained these shells from 

 the surface of the desert to the bottom of the well.^ Again, in 

 suggesting relations between Conrad's and Gould's forms with 

 Bittium^ a genus belonging to the brackish-water division or sub- 

 family (Potamidinae) of the Cerithiidae, he seems to have overlooked 

 the fact that the longitudinally plicated sculptiire of his species is 

 a character common also to the brackish-water genus Gerithidea^ 

 which belongs as well as Bitlium to the Potamidinae.^ 



Had Stimpson's generic definition of Tryonia been more ample 

 I should have been tempted to have given the shell herein dis- 

 cussed a place in said group rather than Fyrgula, which latter, as 

 figured by the Adams and Chenu, shows an angular termination 

 to the aperture at the base of the columella, indicative of a more 

 pronounced feature in the soft parts (siphonal) at this point than 

 the rounded aperture of Tryonia and Tricula (as figured), and 

 the form before me presents. This, however, is a somewhat vari- 

 able feature as between individuals of the same species, and still 

 more so between forms of one species as compared with forms of 

 another. 



With the concurrence of Prof. Call, I have described the shells 

 received from him and Mr. Clark as follows : 



Genus PYRGULA Cristoforo and Jan. 

 Fyrgula Nevadensis, n. s. 



Shell small, elongated, ovate-conic, turreted ; number of whorls 

 five to six (5-6), with a conspicuous keel following 

 spirall}' the periphery of each and terminating near 

 the middle of the outer edge of the continuous peri- 

 treme, which is otherwise simple, ovate and slightly 

 effuse, and appressed (to the whorl) above; in some 

 specimens somewhat produced on its inner side and 

 suggesting a faint umbilicus. Shell white or nearly 

 so ; smooth and glossy, with a slight epidermis on 



' For further information on this point, see my remarks on the "Fossil 

 Shells from the Colorado Desert," in Am. Naturalist, March, 1879. 



^ The connection of the marine Cerithiidse with the fresh-water Melaniidae 

 through the brackish-water Potamidinae, seems natural and logical. In this 

 connection the remarks of Swaiuson in his "Treatise on Malacology," are 

 well worth perusing. 



