112 CYCLADIDiE. 



is chiefly superior, and the diminution of it on either side of 

 the beaks takes place without any marked inequality, or 

 any flattening of the surface adjacent to the dorsal slopes. 

 The valves are regularly girt with more or less closely-dis- 

 posed elevated concentric striae, which are very manifest 

 below and anteriorly, but usually become obsolete upon the 

 umbonal region. The colour of the glossy epidermis is 

 brownish-green, with usually two or three darker zones, and 

 occasionally (but rarely) some indistinct dusky linear rays 

 towards the ventral margin, near which latter the surface 

 almost invariably assumes a yellower cast. Both extremi- 

 ties are rather broad ; that of the slightly shorter anterior 

 side is more rounded than the hinder termination, which 

 has a tendency to biangulation, although the corners are 

 generally rounded off. The ventral edge is moderately 

 and equably curved ; the declination of either dorsal edge 

 is but trifling, and the curvature but slight. The ligament 

 is distinct, and even slightly projecting at its extremity, 

 and is environed and succeeded by a yellowish stain, where 

 the dorsal edge is likewise somewhat flattened. The urn- 

 bones, which are tumid, obtuse, and usually of a paler tint 

 than the prevailing ground-colour, are preceded by a nar- 

 row and not profoundly impressed lunule, which is also of 

 a yellowish hue ; both dorsal markings are occasionally 

 rendered more vivid by a not unfrequent darker stain at 

 both extremities of that margin. The interior is of a 

 bluish-white. 



The ordinary length of the finer specimens is ten lines 

 and a half, and its breadth about two-thirds of an 

 inch. 



The tubes of the animal are tinged with rose or tawny, 

 and when fully protruded are nearly equal, the branchial, if 

 either, being longest. The foot is large, white, and lingui- 



