278 TELLINIDJE. 



still less so, the degree of convexity and inclination in both 

 being in inverse proportion to that of the ventral margin. 

 The anterior side is the narrower, and tapers to a well 

 rounded extremity ; the posterior termination is also 

 rounded, but irregularly so, manifesting in but a very 

 trifling degree that tendency to biangulation which is al- 

 most typical of the genus. The umbonal ridge is per- 

 fectly obsolete ; the beaks are depressed, and the ligament 

 is small, of a yellowish-brown, and by no means promi- 

 nent. The interior is frequently stained with brilliant 

 orange or pur[)le, with a white area or ray beneath the 

 beaks ; it is sometimes livid or lilac, and more rarely 

 whitish, with the external red ray equally visible on the 

 inner disk. The teeth are remarkably small, but re- 

 semble in other respects those of vespertina ; the laminar 

 denticle is, however, rarely if ever present. 



The dorsal edges are often stained with red at irregular 

 intervals, and the ligament is very frequently barred with 

 roseate brown. For size, an inch in length, and a little more 

 than half that space in breadth, may be regarded as a fair 

 average. 



The animal is entirely white ; its mantle is conspicu- 

 ously fimbriated. The siphons are slender, the upper 

 one with eight, the lower with six ciliated ridges ; the 

 cirrhi of their extremities are small. The foot is thick 

 and linguiform. The labial tentacles are lanceolate. When 

 placed in a vessel of sea Avater, with a supply of sand, it is 

 very active, moving about in all directions, and evidently 

 has considerable power of changing place. 



Though formerly esteemed rare, it appears to be a widely 

 diffused and plentiful shell. Whilst it has not been found 

 at such great depths as P. Ferroensis, it appears to be habi- 

 tually a resident in deeper water than that species, and is not 



