DIMYARIA. 141 



transverse teeth, and having at its extremities from two to 

 five small parallel ribs ; ligament entirely external. 



Distinguished from the genus Area, in being more gibbous, the an- 

 terior side obliquely truncated, and Avith an ear-shaped testaceous ap- 

 pendage, placed at the angle of the muscular impression, and forming 

 a chamber or di\4sion. 



Cucullaa aiiricuUfera. — The Eared Cdcull^a. Plate 

 XVI. fig. 10. Obliquely heart-shaped, ventrieose, with 

 decussated striae ; reddish-brown ; hinge with two parallel 

 ribs at each end ; w^hite within, and slightly tinged with 

 violet. Two and a half inches broad. Inhabits the Indian 

 ocean. 



TRIBE IV. CARDIACEA. 



Having the primary teeth irregular, either in form or situ- 

 ation ; and accompanied by one or two lateral teeth for the 

 most part. 



Genus 14.— ISOCARDIA — Lamarck. 



Generic Character. — Shell equivalve, heart-shaped, ven- 

 trieose; beaks very distant, divergent, and spirally turned 

 to one side; hinge with two primary flattened teeth, situ- 

 ated under the beak, and with an elongated lateral tooth 

 under the ligament, which is external. 



Isocardia Cor — The Heart Isocardia. Plate XVI. 

 fig. 11. Globular, and heart-shaped, concentrically wrinkled ; 

 reddish-chestnut or brown, the umbones paler and promi- 

 nent; inside white. Four inches long. Inhabits the Medi- 

 terranean and British seas. 



Genus 15.— HIATELLA Baudin. 



Generic Character. — Shell equivalve, considerably in- 

 equilateral and transverse; gaping at the upper margin; a 

 small cardinal tooth in the right valve, and two oblique 

 somewhat larger teeth in the left valve; ligament external. 



