CRETACEOUS F0S8ILS. 175 



tunity to study the development of the young of C. pyriformis through its 

 various stages of growth. 



This form resembles Mr. Gabb's C. Horuii, though not so closely as 

 the last resembles his C. alceformis. 



Locality and position. — Bear River, mouth of Sulphur Creek, Wyoming, 

 from the same horizon as the last. 



GASTEROPODA. 



AURICULID^. 



Genus RHYTIPHORUS, Meek. 



(piWr, a wrinkle; (>opoV, to bear.) 

 Rhi/liphorus, Meek (1873), Hayden's Sixth Ann, Eep. U. S. Geol. Survey of the Terri- 

 tories, 478. 



The type of this group has the general aspect of Melampus, excepting 

 that it has a series of small, oblique, short folds around the top of the some- 

 what shouldered whorls; while a slight curve in these little folds or costa? 

 indicates the presence of a faint sinus in the lip near the suture, somewhat 

 as in Schizostoma, Lea, but much less deeply defined. It has two folds on 

 the columella, while the outer lip is thin, and apparently entirely smooth 

 within. 



Tyj^e Melampus priscus, Meek, which is the only species known. 

 RHYTIPHORUS PRISCUS, Meek. 



Plate 17, figs. 6 and 6 a. 

 Melampus priscus, Meek {I860), Proceed. Acad. Nat. Sci. Philad., XII, 315. 

 Khytiphorus priscus, Meek (1876), Col. Simpson's Report Expl. across the Great Basin 

 of Utah, 364, pi. v, figs. 4 a, b* 



Shell obovate, about once and a half as long as wide; spire depressed- 

 conical; whorls about five, convex, or faintly subangular; last one large, 

 somewhat shouldered above, and tapering below the middle; suture well 

 defined; surface marked by rather obscure lines of growth, and the small, 

 regvilar, vertical, or slightly oblique folds, which are distinct on the volutions 

 of the spire, and around the upper edge of the body -whorl, but obsolete on 

 all the surface below this; aperture narrow, angular above, and apparently 

 very narrowly rounded below; outer lip sharp and apparently smooth 

 * These are better figures than those here given. 



