99 
CARDIUM decussatum. 
TAB. DLII.—fg. 1. 
Spec. Cuar. Cordiform, antiquated, longitudinally 
ribbed; anterior margin rounded ; posterior 
side a broad area raised in the middle ; length 
and breadth nearly equal. 
Syn. Cardium? decussatum. Mantell, Geol. Suss. 
p. 126. ¢. 25. f. 3. 
Tue form of the posterior side of this Cardium is pre- 
cisely like that of C. cardissa; the keel, however, by which 
it is bounded is obtuse ; the anterior side is much more 
prominent ; it is conical with a rounded margin. The 
beaks are elegantly incurved. 
For this rare production of the Chalk Marl we are 
indebted to the intelligent author of the Geology of Sus- 
sex: the specimen is from a pit at Hamsey; the one fi- 
gured by our friend was found at Brighton. When the 
anterior side is viewed, a general resemblance is obser- 
vable to the genus Pholadomya ; but the posterior side 
is so exactly similar in form to the heart-shaped cockles, 
that, in the absence of all knowledge of the hinge, we 
follow Mr. Mantell in referring this species to Cardium, 
along with the hibernicum. 
