Description of Some Cincinnati Fossits. 



145 



The umbonal sulcus is not well defined, but it seems to 

 straighten the basal margin. The cardinal line is directed at 

 a high angle from the basal margin ; the shell is thick, and 

 the valves are held together by a very strong external liga- 

 ment that is remarkably well preserved in our specimen. 

 There was no gaping of the shell at either end. 



Sphenolium and Orthodesma belong to the same family of 

 shells, and, as at present advised, they will fall into the same 

 family with Or thonota, and, therefore, belong to the Orthonotidcc. 



ORTHODKSMA CVMRfLA 11. Sp. 



Plate 8, Fig. 7, right valve of a nearly complete cast ; Fig. S, 

 left valve of another specimoi ; Fig. 9, cardinal view of the 

 same, the posterior end is broke?!, but there is no evidence that 

 the shell was gaping. 



Shell elongate, about three and a half times as long as wide ; 

 thickness nearly equal to the width, which gives to the shell 

 a subcylindrical aspect, in the middle part, or taken as a 

 whole, including the cuneiform ends, the general form might 

 be called subfusiform. Beaks small, pointed, situated about 

 one-ninth or one-tenth of the entire length of the shell from 

 the anterior end, incurved and approximate. Cardinal line 

 straight posterior to the beaks, and less than one-half of the 

 length of the shell ; anterior end rapidly contracted forward 

 of the beaks, the point of greatest length being directed a 

 little downward below a straight continuation of the cardinal 

 line. Anterior end acute, from which the shell rapidly rounds 

 into the base below. Posterior part gradually recedes from 

 the termination of the cardinal line to near the posterior end, 

 where it is obliquely truncated and terminates in the sharply- 

 rounded postero - basal margin. Posterior umbonal ridge 

 prominent, subangular anteriorly, but becoming more rounded 

 posteriorly, and extending to the postero-basal end of the 

 shell. Anterior umbonal ridge subangular near the beak, 

 where it is well defined, but gradually rounding and spreading 

 below, it becomes obsolete in the basal margin. Body of the 

 valve sharply sinuate on the umbo, between the anterior and 



