wniTE] FOSSILS OF THE FOX HILLS GEOUP. 181 



7. Pinna Idkesi White.* 



This species lias beeu found only at Fossil Eidge, and being new, it has 

 little value lor comparison in this discussion. 



8. Inoceramus ohlongus Meek. 



This is one of the largest and most robust species of the CatiUus section 

 of the genus Inoceramus that is jet known in American strata. Meek's 

 original specimens were obtained from the vicinity of Fossil Kidge, and, 

 so far as 1 am aware, it has not been certainly identitied in any other 

 district, except the vicinity of Morrison, Colo., where Mr. A. Lakes ob- 

 tained some imperfect specimens apparently belonging to tliis species. 

 It is very abundant and generally very large at Fossil Eidge, some of 

 the shells being nearly a foot in length and fully four inches in transverse 

 diameter. The shell substance is comparatively thin, although th6 shells 

 are so large. Most of the specimens were found with both shells in Jux- 

 taposition, as were also those of most of the other associated bivalves, 

 probably indicating that the waters in which they lived and died were 

 comi^aratively still. It is probable, however, that these Inocerami died 

 in the sand into which they had burrowed, and which now forms their 

 stony se]ralchre. The original description of this species is in the form 

 of a brief foot-note to page 297 of the Annual Eei^ort of the United States 

 Geological Survey of the Territories for 1870. It is also described and 

 figured in another i)art of this report. 



9. Inoceramus vanuxemi Meek & Hayden. 



Dr. Hayden originally discovered this species at the Great Bend of 

 the Upper Missouri Eiver, and it seems not to be a common species. I 

 found it only at Fossil Eidge, the specimens being apparently identical 

 with authentic examples of the species from the Upper Missouri Eiver 

 region. This species is not improbably the same as J. sagcnsis Owen, 

 but I defer the discussion of that question until a futiu^e occasion. 



10. Crenella elegantula Meek & Hayden. 



The original specimens of this species, also, were collected by Dr. Hay- 

 den. He obtained them from the valleys of both the North Platte and 

 Yellowstone Eivers, and, so far as I am aware, the species has not been 

 elsewhere found until I obtained it in the valley of Little Thompson Creek, 

 where alone I have found it. Its i^osition there is near' the top of the Fox 

 Hills Group as developed east of the Eocky Mountains in Colorado, but 

 in the original localities it was found in both the Fort Pierre aiul Fox 

 Hills Groups as they are recognized in the Upper Missouri Eiver region. 



11. jSfucula cancellata Meek & Hayden. 



This is a widely distributed species, having been collected at various 

 localities in Dakota, Wjoming, Montana, and Idaho Territories. I 

 found some imperfect examples of it in the valley of the Cache a la 

 Pontbe, and Capt. E. L. Berthoud has sent examples to the office of the 

 Siu^vey from near Golden City, Colo. At both the latter localities it 

 was found in the upper strata of the Fox Hills Group, but Dr. Hayden 

 found it in the valley of the Yellowstone to range as low as the ui)per 

 part of the Fort Pierre Group. 



* This species is uamed in liouor of Mr. Arthur Lakes, of Golden, Colo., and lias not 

 hitherto been descri))ed. It is sometimes near a foot long, slender, sides not angular 

 along the middle nor very convex ; dorsal border longer than the base ; i)osterior bor- 

 der convex, and sloping from about the midtlle far forward and meeting the base with- 

 out an angle. Surface marked with slender, slightly-raised, radiating ribs, extending 

 from front to rear and covering both valves above and in part below the median line. 

 The ribs are nearly of uniform size throughout, except near the beak, but are wider 

 apart behind than iu front. 



