82 [April, 



other.allied species, these angles are truacated, and the opposite costae united 

 by horizontal bars. Perfect specimens would probably shovr other differences. 

 This is, we believe, the first species of this genus found in America. According 

 to Prof. Bvonn, (Index Palaion(olofficus,) five species have been hitherto described 

 from the whole cretaceous sj^stem, two of which were from the Neocomien, two 

 from the green sand, and one from the true chalk. 



Locality and position. Moreau Trading Post, No. 5 of the series. 



SoLEN SUBPLICATUS. Shell very thin and fragile, elongated, cardinal and basal 

 margins straight and parallel ; buccal extremity obliquely truncate, anal end 

 rounded from below, both ends gaping ; beaks nearly at the anterior extremity, 

 not distinct from nor rising above the hinge line. Six to eight broadly rounded, 

 very faint plications radiate from behind the beaks obliquely backwards to the 

 posterior margin, to which they appear to have imparted a slightly waved out- 

 line ; surface marked with faint lines of growth, and minute transverse closely 

 arranged striae, which do not radiate from the beaks, but traverse the shell at 

 right angles to its longitudinal diameter. Length 1-15 inches ; breadth -26 inch ; 

 heiglit '42 inch. 



The fine transverse striae on this shell are only visible under a high magnify- 

 ing power, and appear to have been as well marked on the inside as on the ex- 

 terior, distinct impressions of them being left on internal cast. 



Locality aiid position. Moreau river, No. 5 of the series. 



Tellina gracilis. Shell elliptical, moderately compressed, extremely thin 

 and fragile ; buccal margin rounded ; posterior end contracted, subtruncate, and 

 having a broad obsolete ridge passing from the beaks obliquely backwards to 

 the postero-basal margin ; cardinal border convex before and concave behind 

 the beaks ; lower border forming a regular elliptical curve ; beaks rather de- 

 pressed, and located a little behind the centre; surface marked with fine lines 

 of growth. Length -90 inch ; breadth of left valve -IT inch ; height -60 inch. 



The above description is made out from a single left valve, so attached to the 

 matrix as to show only external characters. 



Locality and position. Mouth of the Judith, in a sandstone supposed to be the 

 same as No. 1 of the series. 



Tellina eqoilateralis. Shell elliptical, compressed, moderately thick, ex- 

 tremities rounded ; anterior end slightly broader than the posterior ; beaks small, 

 not elevated, located a little in advance of the middle ; surface marked with fine 

 'regular concentric lines. Length of right valve 1-15 inches ; breadth -12 inch ; 

 height "57 inch. 



We have of this species but one right valve, showing none of its internal 

 characters. The position of its beaks, as well as its much greater thickness, 

 preclude the idea of its being an opposite valve of the last. 



Locality and position. Same as preceding. 



Tellina ? Cheyenensis. Shell ovate, compressed, very thin ; anterior extre- 

 mity rounded ; posterior end subtruncate or rounded from above, and very 

 obtusely angular below ; base forming an elliptic curve ; beaks somewhat 

 elevated, placed a little in advance of the middle, surface ornamented with fine 

 Hues of growth and numerous small regular concentric wrinkles, becoming mere 

 lines near the beaks and on the extremities. Length -88 inch ; breadth -36 inch ; 

 height -61 inch. 



We have only seen the outside of this specimen. 



Locality and position. Forks of Cheyenne River, No. 4 of the series. 



Tellina scitdla. Shell elliptical, small, thin, much compressed, curved so 

 as to be convex on the left, and slightly concave on the right sides ; extremities 

 narrowly rounded, the anterior end being wider than the posterior; beaks small, 

 nearly central ; base forming a regular elliptic curve ; surface polished, and 

 marked with distinct lines of growth. Length -50 inch ; breadth -13 inch ; height 

 30 inch. 



Locality and position. Moreau River, No. 5 of series. 



