100 PROCEEDINGS OF UXITED STATES NATIONAL MUSEUM. 



While arraiigiug- the fossils of the National Miiseniu, I lately foiuul 

 among other undistributed material a small mass of fossiliferons rock, 

 which bore the label '-50 miles below Salmon Falls, Snake Kiver/' 



Upon breaking up this mass it was found to contain examples of both 

 the S])ecies that were described by Gabb, and also another form that 

 has not hitherto been described. This makes ten species of mollusks 

 that are now known to exist in that formation. 



Although this fauna, so far as it is now known, is a very meager one, 

 it is, nevertheless, ^^ery interesting, because it differs so much from any 

 other fresh-water fauna, either fossil or now living, in ISTorth xVmerica. 

 Tliis difference is all the more remarkable because the fresh-water faun.'E 

 of the Laramie, and the several Eocene groups, all of whiijh are older 

 than the Truckee Group, consist largely of types that are now living in 

 the Mississippi drainage system. 



Illustrations of all the molluscan species that are yet known to exist 

 in the Truckee Group are brought together on Plate V for the purpose 

 of ])resenting them all at a single view. All of them, except the four 

 figures of Latia daUii, are copies of the original figures pul)lished by 

 Meek and Gabb respectively. 



Not deeming it necessary to repeat the descriptions of the species that 

 have already been published, the new form only will be herein de- 

 scribed. 



The names of the others, however, are given in the following para- 

 graphs, together with references to the resi)ecti\ e works in which the 

 species were originally described. 



Alelania sciilptlli.s Meek, V. S. Geol. Sur. lOth I'arallel. Vol. lY, p. 

 195. 



Melania suhscuJ2)tUis Meek, lb., p. 190. 



Melania taylori Gabb. Paleontology of California. Vol II, p. 13. 



Lithasia anfiqua Gabb, lb., p. 13. 



Garinifex {Vorticifcr) tryoni Meek, U. S. (leol. Sur. 40th Parallel. 

 Vol. IV, p. 188. 



Carinifex ( Vorticlfex) hinneyi Meek, lb., p. 187. 



Ancylus umluUitm Meek, lb., i>. 180. 



t^pliazrium ruyonum Meek, lb., p. ISli. 



Spliccrium idahocnse Meek, lb., ]). 183. 



Latm dalUi (sp. nov.), plate V, figures 17, 18, 19, and 20. Shell sub- 

 ovate in marginal outline; irregularly convex above; the posterior por- 

 tion narrowing rai)idly to a small prominent umlio which ends in a very 

 snuill closely incurved l>eak which is turned a little to the right side, 

 and makes about one full volution. Semilunar shelf or septum comi)ara- 

 tively large. Surface marked by many strong irregular concentric un- 

 dulations; but otherwise it is comparatively smooth, being marked only 

 by fine lines of growth. 



Length, 1() millimeters; breadth, 10 millimeters; height, 7 millime- 

 ters. (Museum Xo. 11547.) 



