1856.] 125 



of aperture -37 inch; breadth of do. -21 inch; apical angle convex or nearly 

 regular, dlvprgence (variable) 44. 



This sppcies presents numerous varieties of forna, apparently dependent upon 

 age. In younger individuals the spire is relatively less elevated, the whorls more 

 rounded and the aperture larger and more oblique. In its surface njHrkitigs it 

 also varies greatly, even in specimens of the same size. The carinoe formed by 

 the laiger revolving lines being in some specimens quite distinct, while in others 

 they are scarcely larger than the finer revolving lines which may be seen by the 

 aid of a lens to form, with the lines of growth, a delicate sub-cancellate surface 

 on all parts of the shell. On other specimens, all these surface markings are 

 almost euiirely wanting. 



Locality. Ten miles above Fort Union. 



Melania convexa. 



Shell rather large, much elongated, sub-cylindrical or terete ; volutions (about 

 ten?) fi'it, closely wouud, and increasing very gradually from the apex; surface 

 ornamented by fine lines of growth, ciossed by distinct, regular, thread-like, re- 

 volving: lines, and extremely fine, nearly obsolete revolving striae ; suture general- 

 ly indistincr; aperture apparently ovate ; lip thin, having a broad very shallow 

 sinus helow \h^. suture, and another near the base of the columella. Length 

 about 1-60 inches ; breadth -48 inch; length of aperture -45 inch ; apical angle 

 convex, divergence 21. 



Our b^st specimen of this interesting species consists of seven volutions, and 

 appears to have lost two or three others from the apex ; the aperture is also dis- 

 torted. Tbe larger revolving lines, about seven of which may be counted on 

 the .second volution, are quite distinct, and near one-third as wide as tbe spaces 

 between, while the liner revolving strias are closely crowded, and so small as to 

 be only seen by the aid of a good lens. The divergence of the apical angle, be- 

 low the middle of an adult shell, is noc more than 13", while above, (and in 

 yout)g shells,) it is as mufh as 28 to 30. 



In tlie last number of tbe Proceedings of the Academy, we described a shell 

 resembling this very closely in form, from the Yellow Sione river, where it was 

 found associated, in a loose mass, with fragments of an Ostrea and a small Cre- 

 taceaus species of Oardnim, (C. rarum, Evans and Shumard). Our specimens 

 being worn and imperfect, we supposed, from its associates, it must be a marine 

 shell, and referred it to tbe genus Turrilella, under the name of T. convex i We 

 now think it may possibly be a specimen of this species, from the junction of tbe 

 Cretaceous and Tertiary beds. 



Locality. Bad Lands of the Judith. 



Cerithium Nebrascensis. 



Shell elongate-conical, very slender, whorls (nine?) convex, and ornamented 

 by three revolving rows of sharply elevated granules, placed upon obscure 

 vertical folds; surface marked with very fine lines of growth, crossed by much 

 stronger, elevated, thread-like, revolving lines, two, three, or more ot which 

 may be counted between each row of granules, suture distinct; aperture ap- 

 parently nearly circular, but teiminating below on the inner side, in a small 

 notch. Length about 1 inch ; breadth -29 inch ; apical angle regular, diver- 

 gence 19. 



On the lower part of the body whorl there are three or four small revolving 

 lines, two of the upper of which are sometimes granular, making on this whorl 

 five rows of granules. Between these and the next row above, one of the revolv- 

 ing liiif^s is also minutely granular. Inform and general appearance, this re- 

 semhl it: two or three species described by Deshays, from tbe Paris basm, but on 

 close cmnparison, we find it quite distinct from them all. Amongst existing 

 species, it appears to be nearest C. granulosum, and estuary species from the 

 Western coast of Africa. 



Locality. Near head waters of Little Missouri. 



