DIMYAIRA. 123 



This differs from the other genera of many toothed shells, in having the 

 ligament partially inserted internally, and in being destitute of the angular 

 groove on the exterior of the valves. 



Section * No distinct longitudinal furrows. ** With raised 

 longitudinal radiating ribs. 



Pectunculus glycimeris. — The Delicious Pectunculus. 

 Plate XVI. fig. 8. Suborbicular. umbones produced; finely 

 striated transversely and longitudinally ; covered with a villous 

 skin, under which it is marked with reddish-chestnut spots or 

 bands; inside white, and the margin crenulated. From two 

 to three inches long. Inhabits the British and Mediterranean 



Genus 12. — A RCA. — Linnceus. 



Generic Character. — Transverse, subequi valve, inequilateral ; 

 beaks remote, separated by the area of the ligament ; hinge 

 linear, straight, without ribs at the extremities ; teeth of the 

 hinge numerous, serrated, close set, alternately inserted into 

 opposite valves ; ligament external. 



Section * Lower margin not crenated. ** Lower margin in- 

 ternally crenated. 



Area iVo(^.— Noah's Ark. Plate XVI. fig. 9. Oblong, 

 striated transversely, and longitudinally ribbed ; umbones re- 

 mote, and encurvated ; margin entire and gaping; cream-white, 

 with divergent and zigzag chestnut stripes ; inside white. Two 

 inches broad. Inhabits the American and British seas. 



Genus 13 — CUCULL^A — Lamarck. 



Generic Character. — Equivalve, inequilateral, trapeziform, 

 ventricose ; beaks distant, separated by the area of the ligament ; 

 muscular impressions elevated before; margin angulated, or 

 with an eared produced border; teeth of the hinge straight, 

 very small, and set transversely, with from two to five small 

 parallel ribs ; ligament external. 



Distinguished from the genus Area, in being more gibbous, the anterior 

 side obliquely truncated, and with an ear-shaped testaceous appendage, 

 placed at the angle of the muscular impressions, and forming a chamber or 

 division. 



Cucidlce auriculifera. — TiiE Eared Cucull.ea. Plate 

 l2 



