white.] ANNOTATED CATALOGUE. 41 



authors reported as coming from Jurassic strata in the vicinity of the 

 Black Hills, where they found it associated with TJnio nucalis and other 

 species, which have already been referred to. It is represented on 

 Plate 3. 



It cannot be doubted that various species of Planorbis existed during 

 the whole of the Cretaceous period, but no evidence of the fact has yet 

 been obtained. In the Bear Biver Laramie beds, however, a small, un- 

 described species is known, as already mentioned, which belongs to the 

 subgenus Gyraulus. 



In the Laramie period the genus Planorbis is believed to have flour- 

 ished; not because many examples have been found in those strata, but 

 because the examples which have been discovered indicate that the dif- 

 ferent species which they represent reached a wide range of differen- 

 tiation. Meek & Hay den described Planorbis convolutus* from Laramie 

 strata, in the Upper Missouri River region, which they regarded as of 

 the age of the Judith Biver beds. This species seems to be referable to, 

 or not widely different from, the typical section of the genus as it is 

 known among living forms. It is represented on Plate 27. 



The subgenus Bathyomphalus Agassiz, although not known to be now 

 living in North America, is represented by three species in the Laramie 

 Group ; but it has not been recognized in any strata that are referred to 

 a later date. One of these species was obtained from the Judith Biver 

 beds, and was described by Meek & Haydeu under the name of Planorbis 

 (Bathyomphalus) amplexus;\ and the other, by the same authors, from 

 the Fort Union beds, under the name of P. (B) planoconvexus. % 



Still another species, obtained from the Laramie strata of Southern 

 Utah by Professor Powell, was described by myself under the name of 

 Planorbis (Bathyomphalus) kanabensis.§ All three of these forms are 

 represented on Plate 27. 



Besides the species of Gyraulus that has already been mentioned as 

 existing in the Bear Biver Laramie beds, another was obtained by one 

 of the parties under the direction of Lieutenant Wheeler, from strata 

 that belong to either the upper part of the Laramie Group, or the lower 

 portion of the Eocene. This species I have described under the name 

 of Planorbis (Gyraulus) militaris.\\ It is illustrated on Plate 28. 



A flue large species of Planorbis was described by Mr. Meek from the 

 Bridger Group of Southern Wyoming, under the name of P. utahensis, 

 and also a variety of the same under the name of P. spectabilis.^\ Both 

 these forms are illustrated on Plate 29. 



* U. S. Geol. Sur. Terr., vol. ix, p. 536, pi. 43, fig. 11. 



tU. S. Geol. Sur. Terr., vol. ix, p. 539, pi. 42, fig. 16. 



t U. S. Geol. Sur. Terr., vol. ix, p. 538, pi. 44, fig. 9. 



§ Powell's Rep, Geology of the Unita Mountains, p. 119. 



|| Proceedings U. S. National Museum, vol. iii, p. 159. 



II For Meek's descriptions and figures of these two forms see U. S. Geol. Sur., 40th 

 Parallel, pp. 189, 190, pi. xvii, figs. 13 and 14 ; Simpson's Rep. Great Basin, Utah, pp. 

 266, 267, p]. v, figs. 6 and 7. Also see Expl. and Sur. West of 100th Merid., vol. iv, 

 p. 209, pi. xxi, fig. 8, for description and figures by White. 



