VENUS. 417 



at the skies, and is finely and closely crennlated within. 

 The anterior side, which is rather the shorter, and is well 

 rounded below, appears to project with an upward inclina- 

 tion owing to the rapid declination of the more or less long 

 and incurved dorsal slope. 



The hinder side is sub-angulated below, the angulation 

 becoming less manifest in the older shells ; its dorsal edge 

 is produced, sloping and curved, the elongation declivity 

 and arcuation becoming more marked as age advances. 

 The lunule is sub-angularly heart-shaped, not profound, 

 rather large, pouting in the young, and usually more or 

 less stained with colouring matter ; the lozenge is large, 

 rather profoundly excavated, and generally lineated. The 

 ligament is sunken, and so extremely narrow as scarcely to 

 be visible. The unibones are more or less compressed, and 

 very prominent ; the beaks are remarkably distinct, small, 

 and acute, leaning most decidedly both forward and in- 

 wards. The interior is generally white, but occasionally 

 of a brilliant reddish-purple ; the margins, except the pos- 

 terior dorsal, are minutely but closely and distinctly crenn- 

 lated. The hinge margin is rather broad, and is furnished 

 in the right valve with a subtriangular central tooth, which 

 is the largest of the three, and shelves inward and poste- 

 riorward, being more elevated in front, and diminishing in 

 height as it widens from its somewhat truncated and 

 slightly bifid apex ; preceding this is a small and very 

 oblique laminar tooth, and behind it lies an elongated more 

 or less bifid solid one. In the opposite valve, the central 

 tooth is similarly shelving and the broadest, but the front 

 one, which is curved and subtrigonal, is the most elevated, 

 whilst the hinder one is depressed, linear, and indistinct. 

 The muscular impressions are strongly marked, the pallial 

 sinus is extremely small, and more or less angulated. 



VOL. I. 3 H 



