124 DIM Y AIR A. 



XVI. fig. 10. Obliquely heart-shaped, ventricose, with decus- 

 sated striae ; j-eddish-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 11.— ISOCARDI A.— ia??tarcA. 



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 i^s 

 external. 



Jsocardia 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 — Rl AT ELh A.— Daudin. 



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 strice ; in- 

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

 habits the British seas. 



Genus 16.— CYPRICARDIA.— ZamarcA-. 



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

 or transversely oblong; teeth of the hinge 'ihree, situated under 

 the beaks, and one lateral tooth below the valve. 



