IN CAPTIVITY. 219 



tli09fe of the valves, of a yellow hue. These ribs of 

 the mantle are visible in aculeatum also, but in tuber- 

 culatum they are much more strongly marked, both 

 in form and colom\ The siphons display the same 

 orange hue as the mantle-lips, and have a finer appear- 

 ance than in the other species ; the interior of the 

 orifices, in both, is covered with a layer of white 

 pearly substance, almost luminous. In the foot of 

 tuberculatum^ which agrees in the particulars already 

 mentioned with that of its congener, I observed a 

 beautiful opalescent gleam, when under water. 



I had supposed that they would display then* in- 

 stincts to more advantage if placed in circumstances 

 more accordant to their habits. I therefore first 

 imitated the sandy beach from which the tide has just 

 retired, by laying \^j proteges on a bowl of wet sand ; 

 and afterwards placed them in a large vessel of sea- 

 water, with a sandy bottom of several inches deep. 

 But in neither case was there any correspondent action 

 in the animals ; they did not attempt to burrow, nor 

 were they so active as when in the clean dish. Most 

 of them soon died ; one only, a large specimen of C, 

 aculeatum, lived about ten days, in the circumstances 

 last mentioned, content to lie submerged on the top 

 of the sand; though the siphons, mantle, and foot 

 indicated health, until the last day or two of its life. 

 Sickness is marked, in these animals, by the lax state 

 of the mantle, which permanently recedes from the 

 foot, and gapes ; by the softness of the foot, which is 

 partially protruded; and by the shrinking of the 

 siphons. 



A considerable number of those sent up, we " killed 



