360 Mr. Bulwer on the Isocardia Cor of the Irish Seas* 



kept distended, and in contact with the interior of the valves, by 

 the included water. 



The valves fit so closely that the animal can remain two days 

 or more without permitting a single drop of fluid to escape. 



Locomotion very confined ; it is capable with the assistance of 

 its foot, which it uses in the same manner (but in a much more 

 limited degree) as the Cardiacea^ of fixing itself firmly in the sand, 

 generally choosing to have the umbones covered by it, and the 

 orifices of the tubes of the mantle nearly perpendicular. 



Resting in this position on the margin of a sand bank, of which 

 the surrounding soil is mud, at too great a depth to be disturbed 

 by storms, the Isocardia of our Irish sea patiently collects its 

 food from the surrounding element, assisted in its choice by the 

 current it is capable of creating by the alternate opening and 

 closing of its valves. 



Some of the specimens that had been taken four or more days 

 before they were brought to me, exhibited on dissection the fol- 

 lowing curious appearance : — On removing the mantle from the 

 surface of the shell, a considerable quantity ef shelly matter of 

 the consistence of thick cream, or like moistened plaster of Paris, 

 was discovered ; on a nearer inspection, the interior layers of its 

 shelly covering were found to be deeply corroded in parallel 

 furrows, in some spots so deeply that the brown or outer 

 layers of the shell were laid bare. This shelly matter had under- 

 gone no change but that of trituration. To what cause is this 

 appearance to be attributed ? Are the animals of this species 

 when in a state of starvation, as these probably were, capable of 

 absorbing a portion of their shell (the gluten), and converting it 

 into nourishment ? Or do the animals, when languid and un- 

 healthy, secrete a menstruum that destroys the cohesion of the 

 particles of which their habitations are formed ? In none of the 

 living specimens that I had an opportunity of examining, did I 

 detect any parasite; while in nine out of ten specimens of the 

 Cyprina Islandica from the same neighbourhood, I found a small 

 Hirudo lurking under the mantle of each, and in very many spe- 

 cimens of a Modiola from the shallow water of the same coast, a 

 small crab (Pisa) shared the habitation with the animal. 



