420 MOLLUSCA. CARDIADjE. Isoqardia. 



land, and those of the Mediterranean examined by Poli. " The foot of the 

 Mediterranean species is much less pointed, shorter, less rugose, and of a 

 somewhat different and lighter colour than the same part in our animal. 

 The margin of the mantle in Poli's figure is strongly serrated, and of the 

 same ferruginous hue as the rest of the animal ; in ours it is plain, and in 

 the healthy animal of a bright orange, while its body is of a yellowish white. 1 * 

 Zool. Journ. No. 7- 301. 



EXTINCT SPECIES. 



1. I. minima. — Globose, subdeltoid ; anteriorly slightly truncated, poste- 

 riorly flattened ; cordate. — Sower. Min. Conch, t. ccxcv. f. 1. — Lower Oolite. 



2. I. tener Obovate, with produced beaks ; anteriorly subtruncated, pos- 

 teriorly rounded ; shell very thin, smooth — Sower. Min. Conch, t. ccxcv. f. 2. 

 —Lower Oolite. 



3. T. rostrata Deltoid, ventricose ; anterior side produced, pointed ; pos- 

 terior depressed, round. — Sower. Min. Conch, t. ccxcv. f. 3 — Lower Oolite. 



4. I. sulcata. — Orbicular, deeper than wide, longitudinally sulcated, pear- 

 ly ; beaks remote Sower. Min. Conch, t. ccxcv. f. 4 — London Clay. 



5. I. concentrica— Transversely elongate, heart-shaped, concentrically sul- 

 cated ; shell thin Sower. Min. Conch, t. ccccxci. f. 1 — Lower Oolite. 



6. I. oblonga Oblong, anterior side short, ventral and dorsal margins 



nearly parallel, and almost straight ; rounded retrally — Sower. Min. Conch. 

 t. ccccxci. f. 2. — In Carboniferous or Greywacke Limestone, Cork. 



7. 1. similis. — Transversely, rather oblong, ventricose, slightly flattened ; 

 anterior side small, turned a little up ; edge of the base nearly straight — 

 Sower. Min. Conch, t. Dxvi. f. J. — In Green Sand. Fragments of a shell which 

 occur in the Suffolk Crag have been figured (Sower. Min. Conch, t. Dxvi. f. 2.) 

 as resembling the recent Isocardia cor. They probably belong to the marine 

 diluvium of the Modern Epoch. 



Gen. HIPPOPODIUM.— " Shell equivalve, obliquely trans- 

 verse ; valves inflated, sub-bilobed ; one rugged tooth at 

 the hinge ; and the indication of a small lateral one under 

 the ligament.'" 



1. H. ponderosum.— Gibbose, with irregular obtuse wrinkled ridges. — 

 Sower. Min. Conch, t. ccl. — In Lias. 



Gen. CX. — CARDIUM. Cockle. — Beaks adjacent ; hinge 

 with two umbonal teeth, and a remote lateral one in each 

 valve. 



* Ribs armed with spines or tubercles. 



431. C. aculeatum. — Shell tumid, thin, produced at the anal 

 extremity;, an angular bend behind the ligament, with 21 ribs. 



