154 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Von it'll a Morton i, M. & H. 



Plate 4, figs. 3, <i, '». 

 Venilia Mortoni, Meek aud Hayden (1862), Proceed. Acad. Nat. Sci. Philad., XIV, 27. 



Shell transversely oblong, or subtrapezoidal in outline, gibbous, thick, 

 and strong; base nearly straight, but rounding up in front; dorsal margin 

 parallel to the base, excepting where it declines, at first gently, then abruptly, 

 into the obliquely-truncated posterior; anterior side truncated vertically 

 immediately in front of the beaks, just below which there is a slight sinuosity 

 of outline, as seen in a side-view ; posterior basal extremity very narrowly 

 rounded, or subangular ; beaks very oblique, strongly incurved, gibbous, and 

 placed directly over the anterior; umbonal slopes forming a prominent, 

 rather angular, oblique ridge, from each beak to the posterior basal extremity; 

 lunule and escutcheon impressed, but without strongly-defined margins; 

 surface marked with distinct concentric striae, and stronger, irrregular ridges, 

 the latter of which sometimes pass into regular, rather distant, low varices on 

 the umbones. 



Length, 1.66 inches; height, 1.40 inches; convexity, 1.17 inches. 



This species is nearly related, at least in external characters, to V. Con- 

 radi, Morton, but differs in being more oblique and more depressed at the 

 beaks, which are also placed directly over the more truncated anterior margin. 

 Its dorsal margin is also longer and less sloping than in Morton's species. 

 It will be more readily distinguished from the last by its greater proportional 

 length, less angular umbonal slopes, and rougher surface. 



I have not seen the hinge of this species; but from its form and general 

 external appearance, there is little reason for doubting that it belongs to the 

 genus under which it is placed. 



Locality and j'osition. — Chippewa Point, on the Upper Missouri, near 

 Fort Benton ; from the Fort Benton group of the Cretaceous. 



Veniella sub tumid a, M. & H. 



Plate 17, figs. 5, a, b. 



Cyprina subtumida, Meek aim Hayden (1857), Proceed. Acad. Nat. Sci. Philad., IX, 144. 

 Venilia subtumida, Meek (1SG4), Smithsonian Check-List North Am. Cret. Fossils, 13. 



Shell rather small, transversely subovate, moderately gibbous; anterior 

 side short, narrowly rounded below the beaks; base forming a broad, gentle 

 curve, the most prominent part of which is usually in advance of the middle; 



