GEOLOGICAL SURVEY OF THE TERRITORIES. 497 



and slightly concave in outline above, and the posterior longer and 

 nearly straight, with a greater obliciuity; posterior umbonal slopes 

 more or less angular in each valve, from the beak to the posterior basal 

 extremity; beaks rather i)rominent, and placed about one-third the 

 length of the valves from the front. Surface ornamented by small, reg- 

 ular, concentric ridges, or strong lines and furrows, both of which are 

 more distinct on the right valve than on the left, where they are some- 

 times obsolete. 



Length of largest specimen seen, 0.50 inch ; height, 0.32 inch ; con- 

 vexity, 0.25 inch. 



This shell agrees so very nearly with a form I have described from 

 Hallville, Wyoming, under the name Corbicula? crassateUifonnis, as al- 

 most to raise a doubt whether it may not be really the same species. I 

 have not seen the hinge of the Hallville species very clearly, though 

 some of the specimens seem to indicate that it can hardly be a Corbula ; 

 while those of a larger, but otherwise scarcely distinguishable form, 

 associated with it, are distinctly seen not to have the characters of Cor- 

 hula, but to present nearly the essential features of Corbicula. Even 

 should the smaller of the Hallville si)ecies, however, prove to be a Gor- 

 bidii, I think the form under consideration, which certainly has the hinge 

 of the latter genus, will be distinguished, S[)ecifically, by its suialler 

 size, more convex valves, and more distinctly striated and furrowed 

 surface ; particularly that of its right valve. It is also not so extremely 

 thin a shell as the Hallville species. 



I also have now before me another very closely allied form, from 

 Black Butte Station, Wyoming, and still more nearly like the Hallville 

 shell referred to. So far as can be determined by comparisons with 

 accidentally compressed, and separated valves of the Hallville shell,, 

 showing none of the hinge characters, the specimens of the Black Butte 

 Ibrui would seem only to difier in being much thicker, and more strongly 

 and regularly marked by concentric lines and furrows. Its decidedly 

 inequivalve character may also be another difference, but it is not pos- 

 sible to determine from the separated and compressed valves of the- 

 Hallville species, yet seen, whether it is inequivalve or not, though it 

 seems not to be. Compared with the form here described, and which 

 must occupy a much lower position in the series, the specimens from 

 Black Butte ditfer chiefly in being much larger, thicker shells, some- 

 what more abrupt on the anterior slope, with more elevated beaks. 

 There may also be differences in the hinge and muscular and pallia! im- 

 pressions, which I have had no opportunity to compare. 



Should this Black Butte form prove to be distinct from both of the 

 others mentioned, it may be called Corbula propinqua. 



Locality and position. — Near Cedar City, Southern Utah, from coal- 

 bearing Cretaceous beds, apparently belonging to the same horizon as 

 the lower part of the coal-series at Coalville. It occurs in great num- 

 bers, associated with Turritella CoalvillensiSj and other forms appar- 

 ently' identical wi th Coalville species. ' 



Neritina (Dostia?) bellatula, Meek. 



Shell small, depressed ovate, or broad slipper-shaped ^ apex very 

 small, and dejiressed to the posterior margin, where it forms one or two 

 minute, slightly oblique, compact turns, that do not project beyond th<3 

 margin, but are sometimes even slightly overlai)ped by it^ inner lip 

 very broad, or shelf-like, and occui)ying more than half of the under 

 side, convex and more or less thickened, with the inner margin concave 



32 GS 



