196 CORBULID^. 



narrow termination. Although semi-transparent, and very 

 far from strong or soHd in texture, yet for its genus it is by 

 no means fragile, as far exceeding in firmness as in size the 

 remaining Neetrct of our shores. The broader portion is 

 extremely tumid, and this ventricosity, which prevails over 

 two-thirds of the surface, is rather suddenly exchanged for 

 compression at the commencement of the beak-like extre- 

 mity of the hinder side. The external surface is not at 

 all glossy, but possesses a kind of silky lustre upon tlie 

 epidermis with which it is covered ; the latter is of a fawn 

 colour, varying in intensity according to individuals, but 

 ordinarily paler towards the beaks, and always of a deeper 

 tint upon the right valve ; beneath it, the shell is smooth, 

 or merely concentrically striolated, presenting no trace of 

 further sculpture. The umbones are excessively oblique 

 and decidedly prominent, and the beaks curve both for- 

 ward and inward ; in front of them the valves are some- 

 what flattened near the dorsal margin. The ventral 

 outline is strongly arcuated, but sinuated near its hinder 

 extremity, where it forms a moderately long, subcentral, 

 straight, and somewhat acuminated rostrum, at its junc- 

 tion with the incurved edge of the posterior dorsal margin, 

 which slopes moderately to its termination. The end of 

 this rostrum is somewhat cylindrical, and a convexly ele- 

 vated, narrow, sub-triangular area runs from it alongside 

 of the upper margin of the shell ; the anterior end is some- 

 what attenuately rounded, with its u^iper edge a little 

 convex and greatly declining. The interior is of a some- 

 what pearly white ; the ligament, which although external 

 is so depressed that one hardly perceives its existence until 

 the valves are opened, is situated in a narrow triangular 

 cavity of the hinge margin in one valve, and immediately 

 beneath the beaks ; the minute cartilage lies in a y^xy 



