68 PHOLADIDiE. 



although far less broad in some individuals than iu others, 

 and generally narrower than in the two following species, is 

 never slender and produced, as in hlpennata. In specimens 

 which have advanced to maturity under circumstances ap- 

 parently favourable to the developement of the natural pro- 

 jiortions, the distance from the beaks to the ventral apex 

 decidedly exceeds that from the angular tip of the triangle 

 to the opposite edge of the auricle. The lower edge of 

 the anterior side is straight, and inclines but very slightly 

 hinderward, forming with the lower posterior one, which 

 slopes (at first somewhat retuscly, and then a little con- 

 vexly) to meet it, a rather blunt but gradually attenuated 

 apex. The auricle, which is never peculiarly large, rarely 

 exceeding the size of the front triangle, is always situated 

 higli up on the posterior side, its base being nearly on the 

 same level with that of the triangular area : the lower pos- 

 terior margin is consequently longer in proportion than in 

 the two succeeding species. It is ordinarily rather narrow, 

 is more or less ear-shaped, and although usually a little be- 

 low the level of the beaks, will occasionally be found rising 

 slightly above them ; but even in that case no risk is in- 

 curred of confounding it with megotara^ as the auricle in 

 that species descends likewise far below the base of the 

 triangular area. No abrupt lowering of surface indicates, 

 as in navalis, its anterior commencement ; a slight conca- 

 vity precedes its terminal reflexion. Internally it is sharply 

 defined by a more or less oblique carina, which, although 

 projecting near the beaks a little over the inner disc, neither 

 forms a continuous shelf-like ledge, nor an appressed over- 

 lapping margin. Both dorsal edges arc concave; the front 

 one is decidedly sloping, and not remarkably abbreviated. 



The texture is tolerably firm, and in large specimens even 

 solid ; the surface is rather glossy, and covered, in fine and 



