272 [November 



Locality and position. Bad Lands of Judith River ; in a sandstone, the posi- 

 tion of which is doubtful, but probably No. 1 of the series. 



Tellina subtoetuosa. 



Shell elliptical or narrow ovate, compressed ; anterior end rounded ; posterior 

 side obliquely truncate at the extremity, and having (in the cast) an obscure 

 ridge passing obliquely backwards and downwards from the beaks ; base forming 

 a broad curve, a little more prominent before than behind the middle ; beaks 

 small, very slightly elevated above the dorsal margin, located a little in advance 

 of the center; surface unknown. Length 2*23 inches; height 1'27 inch; 

 breadth (of left valve) about -22 inch. 



The only specimen of this species we have seen is an internal cast of a left 

 valve, with a few fragments of the inner laminte of the shell adhering. On these 

 fragments indistinct traces of radiating lines are visible, though they may have 

 had no connection with external markings. The anterior muscular impression 

 is narrow ovate, placed near the front margin, with the narrow end above, and 

 slightly inclined backwards. The posterior muscular impression is round ovate, 

 located near the upper margin, and about one eighth the entire length of the 

 shell in advance of the posterior extremity; the narrower end being above and 

 inclined obliquely forwards. Sinus of the pallial impression deep, nearly hori- 

 zontal and apparently rounded at the end. From the inward warping of the 

 back part of the lower border, and the general flatness of this valve, it is pro- 

 bable the other was more convex. 



The compressed narrow elliptical form, and slightly elevated beaks, will dis- 

 tinguish this from all the other species known to us from the Nebraska forma- 

 tions. 



Locality and position. Mouth of Judith River, from a sandstone supposed to 

 be No. 1 of the series. 



Venus ? circulaeis. 



Shell very thin, subcircular, rather gibbous ; cardinal border rounding from 

 the beaks ; extremities and base rounded ; beaks located about half way between 

 the center and the buccal border, elevated, pointed, incurved and directed ob- 

 liquely forwards ; muscular impressions very faint, anterior one almost marginal, 

 and near the beaks ; surface ornamented with fine concentric lines ; sinus of the 

 pallial impression funnel shaped, the apex being directed obliquely upwards 

 towards the beaks. Length -74 inch ; height '67 inch ; breadth -45 inch. 



Not having seen the hinge of this species, we refer it with doubt to the above 

 genus. It may be distinguished from any of the allied Nebraska forms known 

 to us, by its greatest diameter being from the beaks obliquely downwards to a 

 point a little behind the middle of the base, and by its more elevated, pointed, 

 gibbous and oblique beaks. 



Locality and position. Just above the mouth of Milk River, No. 4 of the section. 



Cttheeea pellucida. 



Shell extremely thin and fragile, broad ovate or subcircular, compressed ; 

 extremities rounded, the posterior end being a little wider than the anterior; 

 base semiovate or semicircular ; beaks moderately elevated, placed about one- 

 third of the distance from the center towards the anterior end ; surface marked 

 with fine regular concentric striaj ; muscular impressions very faint ; sinus of 

 the pallial impression triangular, longer than wide, not quite reaching the 

 middle of the shell, and if continued across would strike the opposite border 

 below the beaks. Length (of ovate variety) 1 inch ; height -83 inch ; breadth 

 40 inch. 



Amongst the shells we refer to this species, there are two varieties of form, 

 one being less compressed and more nearly circular, with more gibbous beaks 

 than the other ; but as there are some intermediate forms, and they agree in all 

 other respects, we are at present inclined to regard them as identical. More 



