TRIBE ARCACEA. 151 



obliquely grooved, the valves carinated ; anterior side the shorter, 

 smooth and depressed. An. Var. ? Sojv. G. J". 3. — Reeve, 

 t. 78. f. 3. Ribs closer and as well as the umbonal ridge, more 

 obtuse. 1. — China and the Indian Ocean. 



I. Semisulcata. Lum. 4. Heart-shaped, thin, semi-trans- 

 parent, white, transversely striated ; anterior side with ten longi- 

 tudinal grooves.'^ 



TRIBE ARCACEA. 



Primary teeth small, numerous, and disposed in a line in each 

 valve, which is either straif/ht arched or brohen, the teeth of 

 one valve fitting into the intermediate sjyaces oj' the other valve. 



CUCULLEA. 



Equivalve, inequilateral, trapeziform, ventricose ; beahs distant, 

 separated by the area of the ligament; anterior muscular 

 impression elevated, its margin angulated, or with an eared 

 produced border ; teeth of the hinge straight, very small, and 

 set transversely, with from two to five small 2>C'^'(ill(:l fibs; 

 ligament external. 



C. AuRicuLiFERA. Lam. 1. — Sow. G. — Reeve, t. 81._/. 1, 

 2, 3.— Arca Cucullea. Gmel. 3311.— TF. t. 9. /. 16.— A. 

 CoNCAMERATA. D. p. 22,2.— E. t. 304 .— CL f. 526, 7. Ob- 

 liquely heart-shaped, rhombic, cinnamon colour, ventricose, decus- 

 sated by strife of which the longitudinal ones are the stronger ; 

 within whitish, stained anteriorly with reddish or pale violet brown, 

 with a laminar appendage proceeding from under the beak ; hinge 

 with two large teeth at each extremity. 2 J . . 3}. — Nicobar Isles. 



ARCA. 



Transverse, svbequivalve, inequilateral ; beaks remote, separated 

 by the area of the ligament; hinge linear, .straight, without ribs 

 at the extremities ; teeth of the liinge numerous, arranged in a 

 row, serrated, close set, alternately inserted into opposite valves ; 

 ligament entirely external. 



2 For this species Deshayes proposes the establishment of the 

 genus Cardilia. Oval-oblong, longitudinal, heart-shaped, ven- 

 tricose, the beaks large and prominent ; hinge with a small car- 

 dinal recurved tooth, a pit at the side and a spoon-shaped pro- 

 jection for receiving an internal ligament : anterior muscular scar 

 rounded and superficial, the posterior placed on a thin horizontal 

 plate which projects from beneath the hinge. 



