62 GLAUCUS ; OR, 



the massive shells against the sides, or roll them 

 irregularly over each other. 



" It was curious to notice the extent to which 

 the interior of the cockle was revealed, when the 

 mouth gaped, and the foot was thrust out. By 

 the aid of a candle we could see the interior 

 surfaces of both valves, as it seemed, almost to 

 the very backs. I say, as it seemed, for so thin 

 is the mantle where it lines the shell, and so 

 closely does it adhere to it, that every character 

 of the valves, whether as regards color or ir- 

 regularity of surface, was distinctly visible ; and 

 thus we were able to distinguish the species, 

 not only by their external marks, but by one 

 character drawn from the interior, — the ribs 

 in tuberculatum extending only half-way across 

 the valves, while in aculeatum they reach back 



to the beaks The former is much the 



finer species ; the valves are more globose and 

 of a warmer color; those that I have seen are 

 even more spinous. The mantle is of a rich 

 deep orange, with elevated ribs, corresponding 

 to those of the valves, of a yellow hue. These 

 ribs of the mantle are visible in aculeatum also, 

 but in tuberculatum they are mucli more strongly 

 marked, both in form and color. The siphons 



