420 MOLLUSCA. CARDIAD^. Isocardia. 



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 iigui-e is strongly serrated, and of the 

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

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

 Zool. Journ. No. ^, 361. 



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 vei-y thin, smooth. — Sower. Min. Conch, t. ccxcv. f. 2. 

 —Lower Oolite. 



3. T. Tostrata. — 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. oJ/ore^'a.— 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. ). — 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 maritie 

 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. ex. — 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. 



