66 TESTACEOUS MOLLUSCA. 



edge curvilinear ; valves very but unequally convex, nearly smooth ; 

 inside yellowish white, covered with radiating lines finely indenting 

 the edge : ligament minute : hinge with two diverging cardinal teeth 

 and an anterior lateral in one valve, a single cardinal in the other. 

 T. Iris. Say. Jour. A. N. S. Phil. 2 p. 302. Oblong-sub- 

 oval, very thin, pellucid, compressed, irridescent, white with gene- 

 rally a rosy disc and one or two anterior rays, with numerous 

 minute concentric wrinkles and minute oblique strong equidistant 

 strise, which are abbreviated before and do not reach the narrowed 

 and sub-acute anterior end : ventral edge straight opposite the 

 beaks, -f^ . . ■^^. — U. States. 



T. Alternata. Say. Jour. A. N. S. Pldl. 2. p. 275. — Say. 

 Am. C. t. 65. /". 1. Oblong, compressed narrowed and angulated 

 anteriorly ; white with numerous parallel equal equidistant trans- 

 verse striae which are alternately obsolete on the anterior margin ; 

 anterior dorsal edge sloping somewhat concavely to an obliquely 

 truncated tip, inside tinged with yellow: anterior cardinal tooth 

 eraarginate, with lateral teeth, the posterior one approximate. 1^ . . 

 2^.—U. States. 



T. Crystallina. Chemnitz./. 1948.— TF. t. 3. f. 10. In- 

 equivalve, one valve flat, the other convex ; triangular-ovate, thin, 

 white with raised distant concentric striae, the ventral edge rounded: 

 anterior dorsal edge nearly straight and sloping, posteriorly rounded 

 and rather the longer : a strongly marked fold in one valve, a cor- 

 responding indentation in the other : slopes incurved : two lateral 

 teeth in the flat valve, f . . 1. — Allied to Belcheri. 



T. SoRDiDA. Couthouy. Bast. J. of N. H. 2. tab. 3./. 11.— 

 Sangui. S. Gould, p. 67.- — Oval- compressed, whitish under a 

 horn-coloured epidermis, lines of growth numerous and distinct, 

 posteriorly rounded, .anteriorly shorter and slightly angular: 

 within, semi-irridescent milk-white, hinge with a simple and bifid 

 primary tooth in one valve, teeth usually obsolete in the other, a 

 distant inconspicuous lateral tooth in each. !§ . . ^^. — Boston. 



T. Serrata. Phil. p. 25. — Costa, p. xvii. no. 8. — T. Sul- 

 cata. W. G. C. t. 47./. \.—D.p. 89.— Tr. t. 4./. 63. Ovate- 

 triangular, equilateral, thick, dorsal edges nearly straight in their 

 slopes ; anteriorly angulated, whitish but milk-white within, with 

 raised transverse striae which become lamellar at the angle which 

 bounds the hollow anterior slope which is smooth and narrow : two 

 cardinal and two lateral teeth in one valve, two cardinal only in the 

 other. 1^ . . 1^. — Mediterranean. 



T. Calcarea. Chem. f. 135.— Z>. t. 93.— TF. t. 4. /. 43. 

 Ovate, very brittle, white, glabrous, shorter slightly sub-angulated 

 and inflected anteriorly, narrower and rounded posteriorly : a 

 rounded cleft tooth in one valve shutting into a cavity in the other. 

 1 . . 14-. — Iceland. 



