472 CYPRINIDiE. 



ISOCARDIA, Lamarck. 



Shell inflated, heart-shaped, equlvalve, rather strong, 

 smooth, or furrowed, with or without an investing epider- 

 mis ; beaks very prominent and contorted ; margins en- 

 tire ; muscular impressions small, no pallial sinus. Hinge 

 composed of two erect primary teeth (one of them indented) 

 parallel with the margin in one valve, and three in the 

 other ; a lateral tooth and tooth-like socket. Ligament 

 external, furcated anteriorly. No defined lunule. 



Animal shaped like the shell, oj)en in front for the hroad 

 triangular, compressed, pointed foot. Siphonal orifices 

 sessile, their margins fringed. ^Mantle double edged. 



This remarkable genus may be regarded as constituting 

 a connecting link between the Cyprinida and Cardiadtz^ 

 whilst its aflftnities with Chama and its associates are also 

 not small. Our only British species is rather an excep- 

 tional form, and isolated from its tropical congeners by the 

 possession of a highly developed epidermis. In British 

 strata even as old as the oolitic formations, we have fossil 

 examples of Isocardiee, but all of them bear more resem- 

 blance to those now existing in the seas of warm regions, 

 than to that about to be described. 



I. COR, Linuffius. 



Plate XXXIV. f. 2, and (Animal) Plate N. f. 6. 



Lister, Hist. Conch, pi. 275. — Gualtieri, Lidex Test. pi. 71, f. 



E. — GiNANNi, Opere Postume, vol. ii. pi. 19, f. 129. — 



Knorr, Delices des Yeux, pt. vi. pi. 8, f. 1. 



C'arilium humanum, Linn. Syst. Naturae, ed, 10, p. G82 (bad!}-). 



Chama cor, Linn. Syst. Nat. ed. 12, p. 1137 ; Mus. Ulricaj, p. 510. — Mont. 



Test. Brit. pp. 134, 578, and Sup p. 50. — Donovan, Brit. 



Shells, vol. iv. pi. 134. — Laskey, Mem. Werner. See. vol. i. pi. 



8, f. 7 — Turt. Conch. Diction, p. .32, pi. 17 — Brown, Mem. 



