388 DESCRIPTIONS OF NEW SPECIES OF FOSSILS, 



lines of growth, apparently destitute of undulations, structure fibrous, fibres coarse 

 and angular. 



The only specimen we have of this fossil has an appearance as if the two valves had 

 been crushed in the direction of the length of the shell, presenting a view of the ante- 

 rior end. We refer this specimen to the genus Inoceramus, for the reason that the 

 shell is fibrous in its texture, being thicker towards the margin and thinner towards 

 the beaks, precisely similar in these respects to the external fibrous portions of the 

 shells of this genus. 



In its surface markings this shell differs from any cretaceous species hitherto de- 

 scribed, so far as known to us, either in this country or in Europe ; and more resembles 

 the Liasic and Oolitic species as figured by Goldfuss ; and in its surface marking it may 

 be compared with I. laevigatus^ (Munster) Goldfuss, Petrefacta, II., p. Ill, ta. 109, 

 fig. 6. This species is associated with I. fragilis and Ammonites percarinatus. 



Locality and Position. On the Missouri River, five miles below the mouth of 

 Vermilion River. Lower part of division No. 2 of Section. 



INOCERAMUS FRAGILIS, n. sp. 

 PLATE II. FIG. 6, a, I. 



Shell small, thin, obliquely rhomboid-obovate, height a little less than length ; beaks 

 acute, pointed forward ; hinge line straight, or slightly concave, extended somewhat 

 less than the length of the shell ; forming a nearly right angle with the anterior side ; 

 marked by comparatively strong undulations, which expand upon the body of the 

 shell, and become less prominent towards the base ; surface of the shell marked by finer 

 concentric lines. 



The shell of this species is extremely fragile, and appears to be fibrous throughout its 

 entire thickness. In general appearance it resembles the Inoceramus mytiloides of Man- 

 tell, as figured by Roemer, but the hinge line is more extended, and forms a more obtuse 

 angle with the anterior side, and the height is proportionally greater. It differs ex- 

 tremely from the /. mytiloides as given by Goldfuss ; and it also differs widely from 

 D'Orbigny's figures of I. problematicus, which Roemer regards as identical with 

 I. mytiloides of Mantell. 



Locality and Position. On the Missouri River, five miles below the mouth of 

 Vermilion River. In the lower clay beds of division No. 2 of Section ; associated 

 with a small species of Ammonites, etc 



