ISOCARDIA. 7 1 



With so much strength was the water in some instances 

 ejected, that it rose three inches above the surface of the 

 superincumbent fluid. Animal, small in proportion to its 

 shell, occupying when dead barely a third of the space en- 

 closed in the valves. Its mantle is slightly attached to the 

 shell, and to the epidermis at the margin, and appears to be 

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

 by the enclosed 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 assist- 

 ance of its foot, which it uses in the same manner (but in 

 a much more limited degree) as the CarcUacea, of fixing itself 

 firmly in the sand, generally choosing to have the umboes 

 covered by it, and the orifices of the tubes of the mantle 

 nearly perpendicular. 



" Eesting 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 suiTounding element, 

 assisted in its choice by the current it is capable of creating 

 by the alternate opening and closing of its valves.'^ 



