TAPES. 385 



lunule ovfito-lanceolate, often coloured, and not sunken or 

 well tlefined ; the umbones depressed, and the beaks small, 

 inflected and leaning a little forward. The interior is of a 

 chalky-white, with often a violet or purple stain at the pos- 

 terior extremity. The pallial sinus is very large. 



The teeth, as regards being cloven or simple, are, as usual 

 in this genus ; viz., the two last of the right hinge and the 

 two first of the left more or less bifid ; they are, however, 

 peculiarly elevated and narrow, the central one of the left 

 valve not exceeding (as in decussata,) the other two in 

 breadth. They lean outwards, their inner sides being re- 

 markably curved, and the supporting portion of the hinge- 

 margin arching out below, and bulging out in front much 

 beyond the level of the remainder. 



The length of our largest specimen is about two inches, 

 and its breadth one inch and a quarter ; these dimensions, 

 however, are but rarely attained to, the majority of ex- 

 amples being about an inch and a half only in length, and 

 of proportionate width. 



Animal oblong, thick, yellowish-white or tinged with 

 pink, the extremities of the siphons variously tinged with 

 brown, black, red, or orange. Mantle freely open in front, 

 plain at the edge except for a short space around the ante- 

 rior end. Tubes united for half their length, and then 

 diverging ; the upper or anal one smallest. Their orifices 

 are fringed ; the branchial with from nine to fifteen ciliated 

 rays, and the anal with from fifteen to twenty-five. The 

 foot is linguiform, fleshy, flat-heeled, and furnished with a 

 byssal groove. The palps are of moderate length, narrow 

 and triangular. 



We have often compared the animal of the ordinary or 

 puUastra form of this species with that of the " Vemis jjer- 

 forans,'''' but could find no distinctions. As long ago as 



VOL. I. 8 D 



