124« DIM Y AIR A. 



XVI. fig. iO. Obliquely heart-shaped, ventricose, with decus- 

 sated striae ; reddish-brown ; hinge with two parallel ribs at each 

 end ; white within, and slightly tinged with violet. Two and a 

 half inches broad. Inhabits the Indian ocean. 



TRIBE IV. CARDIACEA. 



Having irregular primary teeth, both in form and situation ; 

 and accompanied by one or two lateral teeth for the most part. 



Genus U.— ISO CARDl A.— Lamarck. 



Generic Character. — Equivalve, heart-shaped, ventricose; 

 beaks very distant, divergent, and spirally turned to one side ; 

 hinge with two primary flattened teeth, situated under the beak, 

 and with an elongated lateral one under the ligament, which is 

 external. 



Isocardia Cor. — The Heart Isocardia. Plate XVI. fig. 



11. Globular, and heart-shaped, slightly wrinkled longitudin- 

 ally ; reddish- chestnut, the umbones paler and prominent ; inside 

 white. Four inches long. Inhabits the Mediterranean and 

 British seas. 



Genus 15 HIATELLA.— Dawcfm. 



Generic Character. — Equivalve, considerably inequilateral 

 and transverse ; gaping at the lower margin ; teeth of the hinge 

 small, in the right valve ; and two oblique somewhat large ones 

 in the left valve ; ligament external. 



Hiatella arctica.— The Arctic Hiatella. Plate XVI. fig. 



12. Transversely oblong ; the apices truncated, with two diver- 

 gent spiny ridges ; yellowish-white, with decussated striae j in- 

 side pearlaceous. Half an inch long, and one inch broad. In- 

 habits the British seas. 



Genus 16.— CYFRJCARBIA.— Lamarck. 



Generic Character. — Free, equivalve, inequilateral, oblique, 

 or transversely oblong ; teeth of the hinge three, situated under 

 the beaks, and one lateral tooth below the valve. 



