444 MOLLUSCA. VENERID^. Cyprina. 



Brit. 114. — C. isl. Turt. Biv. Brit. 135. — Not uncommon on all parts 

 of the coast. 



This is the largest British bivalve shell, measuring sometimes 13 inches 

 in circumference, and, exclusively of the animal, weighing upwards of 9 

 ounces ; it is slightly truncated retrally ; the ligament at the beak is lodged 

 in a deep cavity ; there is no lunette in front of the beaks. At St Andrew's 

 it is called Daikie, and in Zetland Cuvie. 



511. C. triangularis. — Subtriangular, smooth, with a length- 

 ened cordiform depression in front of the beaks. 



Venus tri. Mont. Test. Brit. 577. t. xvii. f. 3 — C. tri. Turt. Biv. Brit. 

 136. t. xi. f. 19, 20.— South of England and Dublin bay. 



Diameter about half an inch ; yellowish-white ; strong, with a few obsolete 

 concentric ridges ; the beaks are produced, and the slope is nearly equal on 

 both sides ; in one valve two teeth, and a curved lateral one, in the other 

 three teeth and a curved lateral one. 



512. C. minima. — Suborbicular, compressed, with broad, 



smooth, transverse ribs. 



Venus min. Mont. Test. Brit. 121. t. iii. f. 3— C. min. Turt. Biv. Brit. 

 137— Southern coasts of England. 



Length a quarter of an inch, breadth rather more ; flesh-coloured, with 

 two red spots near the beaks, and two near the margin, connected by two 

 white lines ; glossy, strong. Dr Turton assigns to this species only two 

 hinge teeth besides the lateral ones. 



EXTINCT SPECIES. 



1. C. aqualis Uniformly^convex, obcordate, or nearly circular, covered 



with numerous transverse concentric striae ; thick, particularly in the middle ; 

 margin acute, extended, entire ; cicatrix obscure. — Venus equalis, Sower. 

 Min. Conch, t. xxi. — In Crag. 



2. C. angulata. — Obtusely cordate, broader than long, beak short angular, 

 rising on the posterior side, which is slightly truncated, smooth ; margin en- 

 tire ; larger hinge-teeth placed at an angle of about 60°. — Venus ang. Sower. 

 Min. Conch, t. lxv. — In Green Sand. 



3. C. rustica Suborbicular, gibbose, smooth ; posterior side obscurely de- 

 fined, convex, with a thick lateral tooth. — Venus rustica, Sower. Min. Conch. 

 t. exevi.— In Crag. 



Gen. CXXVII. CYTHEREA.— Shell suborbicular or trans- 

 verse, unequilateral ; hinge, on the right valve, of three 

 diverging teeth and one transverse and detached at the 

 side under the lunule ; three diverging teeth in the other 

 valve, with an adjacent transverse cavity anteriorly ; sy- 

 phon marks distinct. 



513. C. chionc. — Shell ovately-subtrigonal, smooth, glossy, 

 with slight concentric lines of growth ; a lanceolate lunule raised 

 in the middle. 



