904 PELECYPODA. [Eulamellibranchia. 



cated ; posterior end dilated, convex and ascending towards the dorsal 

 margin, which is descending in front, angled on meeting the basal 

 margin, which is nearly straight or strongly excavated. Lunule short, 

 cordiform, with numerous vertical lamellse. Escutcheon much im- 

 pressed. Sculpture consisting of 12 to 14 strong scaly radiate ribs, 

 the 6 to 7 anterior ribs smaller, the rest much stouter, rounded ; the 

 interstices narrower than the ribs ; concentric growth-lines numerous, 

 produced at regular intervals into convex scales upon the ribs. Colour 

 yellowish- white, posterior ribs yellowish-pink or dirty-brown. Interior 

 white, porcellanous, sometimes with brown spots, the external ribs 

 marked by shallow grooves. Margins undulating, sharp. Hinge-line 

 oblique, right valve with a very short anterior lateral and 2 long 

 lamelliform cardinal teeth ; left valve with a short anterior and long 

 lamelliform posterior cardinal tooth, posterior lateral short. Liga- 

 ment short, external. Adductor-scars distinct, subequal. Pallial line 

 simple. 



Length, 32 mm. ; height, 18 mm. ; diameter, 19 mm. (large 

 specimen). 



Hob. -North and South Islands of New Zealand, and the Chatham 

 Islands, from below low-water mark to about 50 fathoms. Also 

 Tasmania, Australia. Mediterranean, off Tenerife in 70 fathoms 

 (" Challenger "). 



Fossil in the Pliocene. 



Genus 2. VENERICAKDIA, Lamarck, 1801. 



Venericardia, Lamarck, Syst. A.s.V., 1801, 123. Types : V. imbricuta and 

 F. planicosta, Lam. Cardissa. Oken, 1815; not of Megeiie, 1811. 

 Megacardita, Sacco, 1899. 



Animal with the foot large, bent, compressed, pointed in front, 

 with a groove below, but no byssus. Anal orifice complete ; gills 

 large, united posteriorly ; mantle-borders papillate at the branchial 

 opening. 



Shell rounded trigonal, strongly radially ribbed, the ribs frequently 

 beaded, especially when young ; the lunule minute and deep, the 

 escutcheon linear ; the internal margins crenate ; the hinge with 2 

 transversely striated cardinals in the left and 3 in the right valve, the 

 laterals absent or obsolete, a sublunular pustule present in the left 

 valve. 



Distribution. Northern seas, Mediterranean, west coast of Africa, 

 Indian Ocean, west coast of America, Australasia. &c. 



Fossil. Eocene to Pliocene. 



KEY TO SlTBGENEKA. 



A. Right valve with 3, left with 2 cardinals ; no laterals . . VKNKKK AKDIA, s. str. 



B. Right valve with the anterior and posterior cardinals 



feeble ; left valve with feeble anterior and posterior 



laterals . . . . . . . . . . PLEUROMERIS. 



C. Right valve with the posterior cardinal absent, with a 



feeble posterior lateral ; left valve with a feeble 



anterior lateral MIODONTISCUS. 



