CARDIUM. 



and passing to the ventral margin, some of these are 

 much shorter from front to back, and much wider from 

 side to side than in other directions ; the C. Cardissa is a 

 remarkable example of this form. The form of C. hiber- 

 nicum* is ver}'^ remarkable, its anterior extremity being 

 very wide and obtuse, and its posterior end being narrow 

 and produced into the form of a lengthened beak -like 

 process. 



Little is known at present of the natural affinities of 

 the Genus Cardium ; Trigonia, and Isocardia appear to be 

 most nearly related to it : a strong muscular foot, which 

 enables them to move with considerable rapidity seems to 

 be one of the most prominent characters : in the Trigonia 

 this is so strong, that some specimens of the T. pectinata 

 which Mr. S. Stutchbury laid upon the seat of a boat 

 preparatory to putting them in spirits, leaped over the 

 gunwale and rejoined their old companions. 



The fossil species of Cardium occur in nearly all the 

 fossiliferous beds from the Mountain Limestone upwards. 

 In the Mountain Limestone occurred the C. hibernicum, 

 of which we have already mentioned some peculiarities. 

 But the fossil species are much more numerous in the 

 newer formations, as iii the green sand, London clay and 

 crag in England, and in their contemporaneous beds in 

 other countries. 



• We are informed by the Rev. J. Bulwer that the fossil which hag 

 hitherto been called Cardium hibernicum has no claim to a place in this Genus. 



