UNDESCRIBED FORM OF GASTEROPOD MOLLUSK. 421 



extremity of the body, and almost fusing into the corre- 

 sponding apex of the foot. On its surface, at its lateral angles, 

 are two circular convexities, which nearly meet in a depression 

 at the middle line. These convexities are the vaulted roofs 

 of the crypts which contain the branchiae, the deeper colour 

 of which appears through them. Behind the depression be- 

 tween the branchial convexities is a longitudinal elevation 

 which tapers backward, is bounded laterally by two slight 

 furrows, and is produced by the subjacent visceral mass. 

 Beyond these furrows the margins project over the lateral 

 grooves. The anterior margin of the mantle is convex, pre- 

 senting at its centre a concave incision, where it is also 

 elevated or tilted backwards. Behind the concave incision, 

 and exactly repeating its curvature, a number of opaque, 

 slightly-raised ridges extend across the mantle at equal dis- 

 tances, but becoming fainter, are lost as they reach the 

 branchial elevations. Ten or twelve faint opaque white 

 stripes, which become narrower and fainter as they pass back, 

 diverge from the concave incision along the mantle over its 

 elevations, and are lost about the middle of the back. These 

 stripes are more distinct towards the middle line than at the 

 margins of the mantle. 



The foot corresponds in form with the body. It is some- 

 what narrower than the mantle ; with which it is nearly in 

 contact posteriorly, where the apices of the two structures 

 appear to run into one another. It is transversely rugose ; 

 but smooth along both margins. A mesial furrow extends 

 along its posterior third. In front its margin is concave, and 

 in contact with the oval disk. 



The mantle and foot, but particularly the former, are con- 

 siderably broader than the body ; so as to include between 

 their projecting margins on each side a groove, the bottom of 

 which is formed by the Bide of the body. The grooves are 

 narrow behind, where they arc terminated by (lie fusion of the 



