308 TELLINID^. 



The shape of T. proxima, which is intermediate between 

 that of soUdula and tenuis, is very variable, but when fully 

 developed in specimens of a larger growth, is rather obliquely 

 obovate; but becomes more or less abbreviated slightly sub- 

 trigonal and more oblique in others which have lived under 

 less favourable circumstances. The valves, which are rather 

 thin, and usually much bent, do not appear perfectly equal, 

 one being frequently flatter than the other ; both are, how- 

 ever, more or less shallow, of an opaque and rather dull 

 white colour within and without, and almost smooth, being 

 merely marked with minute concentric wrinkles, chiefly 

 apparent at the sides. They are clothed with an olivaceous 

 or ash-coloured epidermis, which is frequently only present 

 towards the lower margin. The ventral edge, which is 

 greatly arcuated in fi'ont, is scarcely convex, but much 

 ascending behind ; the front dorsal outline, excepting near 

 the beaks, is more or less arcuated or at least convex, whilst 

 the hinder dorsal edge is almost rectilinear or even subre- 

 tuse, curving out very slightly, however, near its termina- 

 tion. The degree of declination in the dorsal margin is 

 not constant, but typically is rather trifling anteriorly, and 

 only moderate posteriorly, but in many specimens these 

 slopes, although still preserving their relative proportions, 

 are much more decided. The beaks (when not eroded) are 

 acute and a little projecting ; they are situated much nearer 

 to the hinder termination, which is bluntly angulated below, 

 than to the rounded extremity of the anterior side, which is 

 consequently much produced. The umbonal ridge, although 

 present, is much depressed and almost obsolete ; the ligament 

 is large and prominent. The hinge margin is rather broad ; 

 there are no lateral teeth, and the primary are very caduc- 

 ous ; when the hinge, however, is perfect, one of the teeth 

 is bifurcated in each valve. The pallial sinus is rather large. 



