272 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



beds containing a mingling of the fossils of the Fox Hills and Fort Pierre 

 groups of the Upper Missouri Cretaceous series; also, from the same horizon 

 on Deer Creek, near Platte River. 



Haminea snbcylindrica, M. & H 



Plate 18, figs 10, a, b. • 



Bulla subeylindrioa, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 270 (not d'Orbigny, 



1847). 

 Bulla speciosa, Meek and Hayden (1860), ib., XII, 185.— Meek (1864), Smithsonian Check-List N. Am. 



Cret. Fossils, 16. 



Shell attaining a large size, extremely thin, narrow-subelliptic ; summit 

 rounded, with a small umbilicoid pit marking the position of the sunken 

 spire ; lower extremity obliquely and narrowly rounded ; aperture very nar- 

 row, somewhat arcuate along the upper three-fourths, rising a little above 

 the summit of the body, narrowly rounded at the upper extremity, and about 

 twice as wide below as at the middle ; inner lip thin, reflexed, and appressed, 

 but leaving a narrow, oblique, umbilical chink passing under it below, con- 

 tinued above as a thin film on the inner side of the body-volution ; entire 

 surface ornamented by obscure lines of growth, crossed by small, impressed, 

 transverse striae, generally separated by somewhat wider spaces, sometimes 

 bearing each one or two smaller impressed lines. 



Length, about 1 inch ; breadth, 0.55 inch ; breadth of widest part ot 

 aperture, 0.23 inch ; breadth of same near the upper end, 0.12 inch. 



This species will be readily distinguished from the following, not only 

 by its decidedly larger size, but by its proportionally more elongated and 

 more nearly cylindrical form. Like the last, it is a very thin shell; which 

 thinness causes the transverse striae to be generally rather well defined on 

 internal casts. The differences of size and form between these shells is 

 certainly not due to differences of age ; the specimens of H. occidentalis being 

 numerous, and the largest of them but little exceeding the size of that rep- 

 resented by our figs. 11, />, and 12, a, which are evidently adults, while the 

 more ventricose and shorter form of that species is constant at all ages. 



As with the last-described species, we had to change the specific name 

 of this shell because d'Orbigny had published a Bulla subcylindrica at an 

 earlier date. From its thinness, and transverse striatum over the whole 

 surface, I am led to refer it, like the last, to the genus Haminea, in which I 



* Fig. 10, a, is from an internal cast broken at the base of the aperture, so as to give an unnatural 

 appearance of a truncation there; while it does not show, as figured, the thin, reflexed, iuner lip. 



