280 TELLINID^. 



umbones, and vary in their intensity with diiierent indivi- 

 duals. These rugse usually become more or less indistinct 

 beyond the ordinary position of the umbonal ridge, (which 

 is almost entirely obsolete,) where the area is adorned by 

 about fourteen obliquely-radiating costella;, which constitute 

 the peculiar feature of the shell. The colouring is beautiful 

 but very variable ; ranging from pale yellow, mottled or 

 specked with small livid-red markings, to purple, merely va- 

 riegated with minute whitish speckles. The ventral margin 

 is decidedly convex or even subarcuated, and rises, but not 

 equally, at both extremities, ascending rather more in front. 

 The dorsal edges scarcely slope downwards ; the front one 

 is the more (though very slightly) convex, the hinder one 

 being almost straight. The anterior side is rather the 

 longer, and is a little tapering and well-rounded at its 

 extremity ; the posterior extremity is likewise rounded, 

 the terminal hinder outline, though arcuated, notwith- 

 standing exhibits some slight traces of the ordinary ge- 

 neric biangulation. The ligament is yellowish brown, and 

 neither large nor prominent. The umbones are depressed ; 

 the beaks small, acute, and scarcely leaning to either side. 

 The interior is polished and usually tinted with a deeper 

 shade of the external colouring, (sometimes with the hue of 

 the peach-blossom,) and is invariably adorned, beneath the 

 umbones, with two short, ray-like blotches of livid-red or 

 purple, (the intervening space being usually pale or white,) 

 one on either side of the beaks, of which the hinder is 

 decidedly the larger, and is evident (more or less dis- 

 tinctly) upon the external surface likewise. The teeth 

 are very small, and consist of a single primary one in the 

 left valve, interlocking between two (of which the front is 

 the more divergent) in the opposite valve. The nymphee 

 project but little. 



