HIPPOPUS. 



almost tubular spines. In one valve there are two com- 

 pressed^ irregular, elongated teeth placed just within the 

 linear margin to which the ligament is attached, and in 

 the other valve a third rather obsolete tooth. Ligament 

 external, marginal. 



There is certainly no genus with whose characters and 

 habits, the shells we have represented at fig. 2. agree so well 

 as with this ; they have been placed in different genera 

 by Lamar(3k, which proves that he has entertained some 

 doubts about their proper situation ; he has at length 

 nnited them with several others of similar general cha- 

 racters in Cardium ; with which, however, they do not at 

 all accord : formerly he had placed them with Cardita, to 

 v/hich, indeed, they are more nearly related, and in our 

 view they prove a manifest affinity between Cardita and 

 IIvppopus. There are only two circumstances in which 

 our fig. 2. difi*ers from Lamarck's Hippopus; the first is, 

 that it is rather a longitudinal than a transverse shell; 

 the other is in the muscular impressions, of which it has 

 one, very distinctly marked but small, and placed close 

 to the nmbo behind it ; this we cannot trace in Hippopus 

 '/iuicfdatus, but it should be remarked, that in many spe- 

 cimens of this shell that we have examined, it has been 

 extremely difficult to trace the muscular impressions, as 

 well as the impression of the muscle of attachment of the 

 mantle ; in fact, the whole forms but one impression sur- 

 rounding the edge at a distance, and becoming larger 

 towards the center, and in one specimen we think we can 

 discover the corresponding impression to the one men- 

 tioned in fig. 2. 



The only recent species known, is the Hippopus macu- 

 latus^ fig. 1 . For the reasons given above, we do not hesi- 

 tate at naming the fossil shell, fig. 2., Hippopus avicidaris'^ 

 there are two or three other fossil species resembling thi^ 

 in general form; such is the H, cymhularis, Cardium cym- 

 bularc, Lam. All these fossils are found near Paris, 



