124 PnOLADID-S. 



whitish, and moderately inequilaterah It is closed and 

 tumid in front, somewhat linearly gaping, and provided 

 with a cup-like appendage behind, which, projecting about 

 three -eighths of an inch beyond the extremity of the shell, 

 and composed of two papyraceous vaulted lamina) of a very 

 pale brown colour, suggests the idea of the attachment of 

 a portion of another specimen to its valves. An oblique 

 line from the umbones, forming a rib internally, divides the 

 surface into two nearly equal parts, the hinder of which is 

 merely marked with broad and not very close concentric 

 wrinkles ; the anterior, however, is again diagonally sub- 

 divided, the portion nearer the beaks being most closely 

 and obliquely sculptured with curling laminar strire, whilst 

 the excessively thin and almost semi-transparent matter, 

 which in the adult fills up the expanded front ventral gape 

 of the immature shell, is perfectly smooth. The ventral 

 margin is nearly straight or but slightly convex ; the hinder 

 dorsal, whose edges being turned outwards cause a lip-like 

 projection near the beaks, is similarly but slightly convex, 

 and is but little inclined. The posterior extremity is 

 obtusely biangulated, the anterior peculiarly rounded. 

 The front hinge-margin, which is elevated above the dorsal 

 line, and at first reflected towards the umbones, again 

 recurves, and forms a kind of crest which is abruj)tly trun- 

 cated posteriorly at the beaks, where it is terminated by two 

 minute somewhat rhomboidal testaceous accessory valves. 

 The hinge is furnished with a rather large, erect, thin, sub- 

 triangular tooth-like lamina in one valve, and a smaller and 

 more caducous one in the other. The subumbonal blade is 

 short, flat, curved, and scarcely exi^anding at the tip. 



The young of this beautiful shell (which stage consti- 

 tutes the Pholas lamellata of Turton) assumes so different 

 an aspect, that few would recognize it from a description or 



