92 PHOLADIDiE. 



in cabinet specimens, being very easily detached, are rather 

 complicated in structure, and are situated dorsally in front 

 of the shell. They are two in number^ covered with a 

 yellow skin, and nearly smooth ; their surface, except cen- 

 trally, is a little depressed ; in form they remind us of the 

 single valves, examined laterally, of that common exotic 

 shell, the Cardmm cardissa. They are not simple plates, or 

 laminjB, as in most of the Pliolades^ but double ; the edge 

 where they fold forming an acute carina, from the intensity 

 of the compression. Each, examined separately and ex- 

 ternally, may be likened to a short wing ; the two longer 

 sides, of which the more produced is arcuated, and the 

 other retuse or incurved, forming a more or less acute or 

 obtuse point at their junction. The posterior extremity, or 

 beak, as it were, resembles the outer angles of a quarter of 

 a circle, beneath which, internally, is a very sharp, tooth- 

 like projection. In front of this the inner margin, which at 

 this point is not greatly compressed, and adapts itself to the 

 shape of the reflected front dorsal edges of the shell, is most 

 strongly incurved, again swelling out, however, near its 

 front extremity, a little beyond the line of the correspond- 

 ing external edge. 



Like the Teredines, it penetrates wood which has been 

 immersed for any considerable period in salt water ; where- 

 in it forms for itself an oval receptacle, or cavity, having a 

 small and single external orifice, and nowhere lined with 

 any shelly deposition* 



The original types were procured by Dr. Turton from the 

 fragments of a wreck known to have been submerged for 

 nearly fifty years off Berry Head, near the entrance of 

 Torbay ; other specimens have been taken by Mr. Clark 

 off Exmouth in floating timber. It is occasionally obtained 

 at Scarborough (Bean) ; Mr. M'Andrew has taken it in 



