INVERTEBRATE PALEONTOLOGY. 317 



This shell will be at once distinguished from the foregoing by its greater 

 thickness, shorter spire, obliquely-compressed body-volution, and the more 

 oblique outline of its outer lip. Its suture is also less deep than in either 

 of the preceding species, owing to the fact that the volutions do not round 

 into it, but slope more immediately below it, nearly in the direction of the 

 general slope of the spire. None of our specimens are in a condition to 

 show whether the immediate apex of the spire was pointed or obtuse. 



The rather more solid appearance of this shell, together with its 

 obliquely-compressed body-volution, the very oblique outline of its outer lip, 

 its short spire, rather shallow suture, and the less rounded outline of the 

 volutions just below the same, all tend to give it a somewhat peculiar aspect 

 from that usually presented by species of this group. Consequently, it is with 

 some doubts that it is placed here. 



In general appearance, it reminds one of a species described by 

 Dr. Stoliczka from the Cretaceous rocks of Southern India (Palseont. Indica, 

 II, 307, pi. xxii, figs, o and 5 a), under the, name Mammilla carnatica; and 

 if that shell can be properly referred to Mammilla (Ruma, as some call it), 

 possibly our species might go into the same group. Specifically, at least, it 

 differs from the Indian form in its rather more depressed general outline, 

 smaller umbilical perforation, and less thickened inner lip abovt} the umbilicus. 

 In all of these characters, however, it differs more widely from the typical 

 forms of Mammilla than Dr. Stoliczka's species does. 



It is possible that the names of this and the preceding species may have 

 to be changed to Euspira subcrassa and E. Occident alls; that is, if Euspira is 

 made to replace Lunatia, as already suggested. 



Locality and position. — Mouth of Judith River, on the Upper Missouri, 

 where it occurs with other Cretaceous fossils in beds elsewhere found to hold 

 a position at the horizon of the top of the Fox Hills group. 



Genus AMAUROPSIS, Morch. 



Synon. — Natica, Amaura, &c. (sp.), of some (not Natica, Ad., nor Amaura, Holler). 



Amaitrojms, Miireh (1857), Nat. Bidr. Belkr. Green]., 81. — H. and A. Adams (1858), Genera Recent 

 Mull., II, 621.— Stinipscm (1860), Smithsonian Cheek-List Shells N. Am., 5.— Stoliczka 

 (18G8), Paheont. Indica, II, 294.— Gould and Biuney (1870), Invert. Massachusetts 

 (2d ed.), 348.— Tryon (1873), Am. Marine Couch., 61. 



Etym. — Amaura; orptc, form. 

 Type. — Natica canaliculata, Gould. 



Shell ovate or subovate, imperforate, or only with a very narrow umbili- 

 cal slit ; spire more or less produced ; suture channeled ; aperture subovate ; 



