TRYONIA. Tl 



Tryonia clatltrata, Stimpsox. — Whirls eight. Longitudinal ribs 

 variable in number, usually about twelve to each whirl. Surface other- 

 wise smooth, or marked with delicate incremental striie. There 

 is no trace of revolving strise or lines. Length 0.2 inch. ^'S* 13°* 



The specimens described are in a semi-fossilized condition, A 



mostly white, though not chalky, but with an ivory-like hard- T^ 



ness. Some of them are translucent, looking as if silicified. ^^^ 



From the circumstances under which they were found, how- 

 ever, it is probable that the species existed within a very recent clathrata 

 period, if not indeed now living. 



Large numbers of specimens were found, in company with other dead 

 fresh-water shells of the genera Physa, Planorhis, A'mnicola, Cyclas, etc., 

 in the basin of the Colorado Desert, Southern California, by Mr. Wm. P. 

 Blake, on one of the Pacific Railroad Surveys. The basin is the bed of an 

 ancient lake, now dry. The specimens collected by him are in the museum 

 of the Smithsonian Institution. {Stimpson.) 



Tryonia clathrata, Stimpson, Am. Journ. Conch. I, 54, pi. viii, f. 1, 1865. 



The figure I have given is not a fac-simile of that of Stimpson. 



Tryonia protea, Gould. — Shell elongate, slender, variable ; whirla 

 seven to eight, rounded, divided by a deep suture, simple or variously orna- 

 mented, and barred with revolving ridges and longitudinal folds ; aperture 

 ovate ; lip continuous, simple, scarcely touching the penultimate whirl. 

 Length of the largest specimen three-tenths, 

 breadth, one-tenth inch. Fig- 140. 



From the Colorado Desert (Gran Jornada), Dr. 

 ■T. H.Webb, W. P. Blake. 



Peculiar from its large size and slender form, 

 though diifering greatly in its relative propor- 

 tions. It differs from all others, in being vari- 

 ously sculptured with revolving ridges and 

 longitudinal folds, like most Melarmv. It varies Amnicola protea. 



greatly also in the relative proportions of length 



and breadth. It is as slender as Amnicola attenuata, Hald., and much 

 larger. This appears to be the same shell as that subsequently described 

 by Mr. Conrad, under the name of Melanla exigua. {Gould.') 



Amnicola profca, . Gould, Proc. Bost. S. N. H. V, 129 (March, 1855); 

 P. R. R. Rep. V. 332, pi. xi. fig. 6—9 (1857) ; Prelim. Rep. App. 

 24 (1855) ; Otia, 217. 



Melania exigua, Conrad, Proc. A. N. S. Phila. VII, 269 (Feb. 1855). 



Two of Dr. Gould's figures are copied in my figure (140). With 

 them maybe compared Fig. 141, which is drawn from a specimen 

 presented by Prof. Haldeman (No. 9143), and pronounced by 

 Mr. Conrad to be his Ilelania exigua, it having been one of 



