MONOMYAIRA. Ill 



the lower valve largest and concave, ligament semi- internal ; the 

 hollow of attachment increasing with age. 



This genus has two sections, * with a simple waved margin, 

 and not plicated, ** margins plicated. 



Ostrea eduUs. — The Edible Oyster. Plate XV. fig. 3. 

 Suborbicular, rugged, with undulated, imbricated scales, and 

 transversely striated ; one valve flat, and the other convex ; 

 outside brownish-green ; inside pearly- white ; exceedingly varia- 

 ble in size. Inhabits the coasts of Europe. 



Genus U.— GRYFH^^ A.— Lamarck. 



Generic Character. — Inequivalve, free ; lower valve largest 

 and concave ; beaks large, projecting, and spirally twisted ; up- 

 per valve small, flat, and acting as a lid; hinge without teeth; 

 the cardinal hollows oblong, arcuated ; having one muscular im- 

 pression. Animal unknown. 



This genus is distinguished from the ostrea by the very deep 

 and crenated lower valve, and in its summit being terminated in 

 a long spirally recurved beak, slightly turned to one side ; and 

 the edge sharp and angular. 



Gryphcea angulata. — The Angulated Gryph^a. Plate 

 XV. fig. 1. Oblong-ovate, with three longitudinal, carinated 

 ribs below ; beak large, somewhat oblique. Four inches long. 

 Habitation unknown. A specimen of this rare shell is in the 

 Museum of the Jardin du Roi, at Paris. 



TRIBE II. PECTINIDES. 



Shell for the most part regular, and not foliaceous ; the liga- 

 ment either interior, or partly so. 



Genus 15.— POD OP SIS — Lamarck. 



Generic Character. — Inequivalve, nearly regular, adhering by 

 its lower beak ; without ears ; the lower valve the largest, con- 

 vex, and produced at the base ; hinge without teeth ; ligament 

 internal. Found only in a fossil state, they nearly approximate 

 the genus Gryphcea, from which they are distinguished by the 

 k2 



