110 CYPEINID^E. 



more limited degree, as the Cardiacete, 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 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 the valves." 



I have been tempted to copy the Rev. James Bulwer's 

 account of this animal from the second volume of the ' Zoolo- 

 gical Magazine/ rather than refer to it, as it singularly corro- 

 borates my views of the mode in which the branchiae of 

 bivalves are supplied with water. That gentleman, after many 

 days' examination, expressly states that the ingress current of 

 water was effected by the opening of the valves, and which was 

 expelled by their closure at the branchial orifice. This state- 

 ment negatives the doctrine of branchial currents by cilia, 

 and ingress and egress currents by separate apertures, that is, 

 by the water being received by the branchial siphon or orifice 

 and discharged from the anal one; besides, this result is 

 anatomically impossible, as all my experiments at least in the 

 closed-mantle bivalves with elongated siphons appear to 

 prove that there is no communication between the anal and 

 branchial tiibes. In this species, the mantle being open, the 

 branchiae receive the water from the great ventral range, and 

 it is expelled by the same channel. 



We are of opinion that the branchial cilia, the motive agent 

 of the water with many authors, have no other function than 

 to divide it, to facilitate the extraction of the vital influence. 



"We strongly recommend those naturalists who advocate the 

 doctrine of branchial currents by cilia and distinct siphons or 

 apertures, carefully to consider Mr. Bulwer's account, who at 

 any rate must be looked on as a disinterested observer, and 

 has no object in supporting a particular theory. 



This genus is artificial, and originates in the shape of the 

 shell ; the animal is so similar to that of Cyprina, that Iso- 

 cardia might very well merge in it. 



