PANDORA. 211 



as permanently characteristic. The ventral margin is 

 greatly arcuated, and swells out chiefly behind, the front 

 portion of it ascending in a much less convex line ; the 

 broadest part of the shell is by no means between the 

 beaks and the opposite margin, but not far from the hinder 

 termination, from whence the width gradually diminishes 

 to the very narrow extremity of the anterior side. This 

 latter is sometimes equal to a third, sometimes to a fourth 

 only, of the length of the posterior side, its superficial in- 

 equality is infinitely greater ; the front dorsal edge is deci- 

 dedly and retusely sloping ; the hinder dorsal margin is 

 straight, and either horizontal or slightly ascending ; the 

 posterior end is by far the broader, being expanded, almost 

 rectangular above, and rounded beneath. The umbonal 

 ridge is obsolete, and the beaks depressed ; the nacre is 

 within of a silvery pearl, and greatly iridescent ; the tooth 

 of the left valve elongated, shelving, subtrigonal, laminar, 

 confined to the anterior side, and truncated behind ; that 

 of the right valve is small, narrow, perpendicular, and cen- 

 tral ; the cartilage is oblique, and not immediately adja- 

 cent to the teeth, but forms an acute angle with them at 

 its apex. 



The size of rather a large example is seven-eighths of an 

 inch in length, and half an inch across at the broadest part. 



Mr. Clark has observed the animal, and describes it as 

 of an elongated suboval form, having the left side much 

 more tumid than the right. The mantle is entirely closed, 

 except a small fissure at the anterior end for the passage 

 of the foot : posteriorly it forms a sheath, from which two 

 very short tubes issue, rounded and very slightly separated 

 at their points ; their extremities have fine white rays, and 

 the tubes themselves are aspersed with exceedingly minute 

 intensely white spots, like grains of sand. [In Mediter- 



