DIMYAIRA. 123 



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

 ligament partially inserted internally, and iu 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, subequivalve, 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 iVocE.— Noah's Ark. Plate XVL 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 j 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 aiiricuUfera.— Tiiv: Eared Cucull^ea. Plate 

 l2 



