INVERTEBRATE PALAEONTOLOGY. 351 



umbilical region, but not covering the low, strongly spiral, umbilical ridge, in 

 crossing which the lines of growth make a backward curve parallel to the 

 outline of the sinus at its lower termination at the base of the aperture. 



Length, 0.77 inch; breadth, 0.58 inch; length of aperture, 0.61 inch ; 

 breadth of same, 0.3G inch ; spire with convex slopes, which diverge at an 

 angle of about 105°. 



I know no other recent or fossil shell so nearly like this as Bullia 

 ampullacea of Middendorff, already mentioned in connection with the generic 

 description; and that differs too decidedly in its specific characters to require 

 critical comparison. 



Locality and position. — Moreau River; from the Fox Hills group of the 

 Upper Missouri Cretaceous series. 



'Genus 0D0NT0BASIS, Meek. 

 Synon.—Fusus and Bucciniim (sp.), Hall and Meek ; but not as properly understood. 



Etym. — otioic, a tooth ; (iaaic, a base. 

 Type. — Fusus constrictus, Hall and Meek.* 



Shell buccinoid-fusiform ; spire more or less produced ; body-volution 

 ventricose, and separated below from the short, narrow beak, by a sharply- 

 defined, narrow, revolving sulcus, that terminates below at the connection of 

 the outer lip with the canal, in a small tooth-like projection ; outer lip thin, 

 smooth within, and nearly straight in outline ; inner lip not thickened, but 

 well-defined ; columella a little twisted, slightly flattened, and bearing two 

 oblique plaits below, the lower one of which is formed by the raised lower 

 edge of the obliquely truncated columella, and the other, which is very 

 obscure, or perhaps sometimes obsolete, placed a little above the same; 

 surface ornamented by vertical folds and revolving lines and furrows. 



The type of this genus is a small buccinoid, or short subfusiform shell, 

 nearly resembling Admete in form and surface-characters, but differing in 

 having the lower part of its aperture abruptly contracted into a little short. 

 oblique canal, rather than a mere notch. A still more important difference 

 is also to be seen in the peculiar, distinctly-defined, narrow sulcus, starting 

 at the connection of the outer lip with the little canal below, and passing 

 around obliquely upward so as to go under the inner lip nearly opposite the 



* In order to prevent the possibility of any uncertainty in regard to the type of this genus, I would 

 state that Fusus constrictus, Hall and Meek, is cited as such, because it is believed to be the same as the 

 species hereinafter described under that name. Should the latter prove distinct, however, it must bo 

 considered the type, as the characters on which the genus was founded were observed in this shell, 

 which has not been directly compared with the typical specimen of Fusus constrictus. 



