220 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



20. Gorbula subtrigonalis Meek & Hayden. 



It has been stated on a previous page that good reasons appear to ex- 

 ist for regarding - G. subtrigonalis Meek & Hayden, C.perundata Meek & 

 Hayden, G. crassatelliformis Meek, and C. tropidopliora Meek, as belonging 

 to one and the same species, the difference being only varietal and prob- 

 ably due to local environment. Mr. Meek's types of the two last-named 

 forms were obtained from the Bitter Creek series of Laramie strata, 

 the former at HaUville and Black Buttes stations, and the latter at the 

 locality two miles below Point of Rocks. The difference between these 

 two latter forms is significant as being similar to that between G. undi- 

 fera and G. subundifera, and also similar to that between other forms 

 from different strata of the Bitter Creek series presently to be noticed. 



21. Neritina volvilineata "White. 



The type specimens of this species were found at Black Buttes Station 

 associated with Melania ivgomingensis, Gorbicula (Leptestlies) fracta, and 

 seven or eight species of Uniones. Yampa Valley is the only other locality 

 at which this species has been discovered. See remarks under that head 

 on a previous page. 



22. Weritina ( Velatella) baptista White. 



In Ann. Bep. IT. S. Geol. and Geog. Sur. Terr, for 1872, pp. 497-499, 

 Mr. Meek described three species of Neritidce from the Cretaceous rocks 

 at Coalville, Utah, for which he proposed the subgeneric name of Vela- 

 tella. In their distinguishing charactistics they approach Velates Mont- 

 fort, but the differences pointed out by Mr. Meek are doubtless of at least 

 subgeneric value. Two of the species described by him were found in 

 the brackish- water layers at Carleton's coal mine, which are both under- 

 laid and overlaid there by marine strata of the Fox Hills Group ; and 

 the other was from marine Cretaceous strata of the same series a couple 

 of miles away from the first-named locality. N. ( V.) baptista is described 

 in Bull. U. S. Geol. and Geog. Sur. Terr. vol. iv, p. 715, and was found 

 in the Laramie strata at Black Buttes Station associated with the pro- 

 ceeding species and its brackish- and fresh- water associates there. This 

 peculiar type has been found at no other than the Coalville and Black 

 Buttes localities, the one in the Fox Hills Group and the other in the 

 Laramie. 



23. Goniobasis gracilienta Meek & Hayden. 



A goodly number of examples were found at the Black Buttes locality 

 which appear to be specifically identical with G. gracilienta Meek & Hay- 

 den, although they are smaller and rather more slender than the types of 

 that species are, and also more slender than those examples are that were 

 found in Crow Creek Valley east of the Bocky Mountains. For remarks 

 on that species see notes on the fossils of the last-named locality. 



24. Gassiopella turricula White. 



This is the type and only species of the genus Gassiopella that has yet 

 been discovered. It has been found only at the Black Buttes locality, 

 where it is associated with Unio, Gorbula, Goniobasis, Gampeloma, &c. 

 Although it is a very interesting form, being unique, it is of little value 

 in the present discussion, which is mainly one of comparison. It is de- 

 scribed in Powell's Report on the Geology of the Uinta Mountains, page 

 133, under the name of Leioplax f turricula, but it was made the type of 

 Gassiopella in Bull. Geol. and Geog. Sur. Terr. vol. hi, p. 606. 



25. Melania ivyomingensis Meek. 



This is one of the finest and most interesting species yet discovered in 



