MALACOZOA. TKOPIOPODA. LAMELLIBANCHIATA. 257 



nent, approximated, curved forwards. Frontal slope eon- 

 cave, with a faint ovate or cordate depression. Hinge very- 

 strong ; the right valve with an anterior depression near 

 the margin, two diverging cardinal teeth, separated by a 

 deep depression, the posterior tooth thick and bifid, an 

 oblique groove, succeeded by a long submarginal ridge, 

 externally of which is an elongated groove extending far 

 along the posterior slope ; the left valve with an anterior 

 crenulate tooth, two thin diverging cardinal teeth, sepa- 

 rated by a broad triangular depression, and succeeded 

 by an elongated groove and a long ridge. Ligament ex- 

 ternal. Muscular impressions rather small, submarginal; 

 paUial impression entire. 



1. Ct/prina Isldndica. Icelandic Cyprina. 



Shell obliquely cordate, roundish-ovate, thick, rounded before 

 and behind, concentrically rugoso-striate, with a sublamellate 

 epidermis; xunbones prominent, obliquely incurved ; a broadly 

 ovate but undefined depression ; inner surface dull chalky, with 

 a broad glossy margin ; epidermis brownish-ohve, abraded on 

 the umbones ; inner surface white. Length five inches and 

 three-fourths, height five inches. 



Young individuals are longer in proportion to their height, 

 and have a pale yellowish-grey or brownish-red epidermis. 



Not uncommon along the sandy coast, and frequently cast 

 on the beach. 



Venns Islandica. Linn. Syst. Nat. ii. 1 131 . — Concha e maxirais, 

 admodum crassa, &c. Lister, Anim. Angl. 173. PI. 4. f. 22. — V'enus 

 mercenaria. Penn. Brit. Zool. iv. 94. PI. 53. f. 47. — Cyprina 

 Islandica. Flem. Brit. Anini. 443. — Cyprina Islandica. Turt. Brit. 

 Biv. 135. — Cyprina Islandica. Lamk. Syst. v. 557; Ed. 2. vi. 

 290.— Venus islandica. Mont. Test. Brit.' 114. 



Genus 3. Astarte. Sowerby. 



Shell equivalve, anisomeral, moderately convex or 

 compressed, subtriangular, roundish or elliptical, con- 

 centrically sulcate, with a dense olivaceous epidermis. 

 Umbones prominent, approximated, curved forwards. 

 Anterior dorsal slope concave, with a distinct cordato- 

 oblong depression, of which the sides slope inwards. 

 Y 2 



