OF THE GENUS CNIO. 261 



liver, intestines, and an arterial and venous circulation, so 

 complete as to excite our greatest admiration. 



Taking the natural position of the animal, I have reversed 

 the anterior and posterior margins as used by Linnaeus, Bru- 

 guieres, Lamarck, Bosc, and others ; and have followed Cuvier* 

 and Blainville. That margin which has the ligament be- 

 tween it and the beaks is considered by Lamarck as the ante- 

 rior margin, but it will be found on examination not entitled 

 to be so considered, for two reasons: 1. The mouth over 

 which is situated the brain is placed in the opposite margin. 

 2. Wlien the animal is in progressive motion, this opposite 

 margin is always pointed in the direction of its progress. I 

 therefore follow Cuvier in his anterior and posterior margins, 

 because they are founded in truth. 



A recent and very accurate wi'iter, Blainville, gives us so 

 simple an explanation of the position in which a bivalve should 

 be placed, that I am induced to extract it. He says — " We 

 suppose the shell to cover the animal, and that it is passing 

 from the observer, the head (mouth) in front. The beaks 

 should be above — ^the ligament between the beaks and the 

 observer. In this position the opposite side to the beaks 

 would be the base, and the two extremes of the perpendicular 

 diameter of this direction would be, the one anterior, the other 

 posterior." 



Of the habits of this animal we know little ; future obser- 

 vations must open to us an interesting history of them. 

 With regard to their food, it seems to be a matter of doubt upon 

 what they subsist. I have strong reasons to believe they feed 

 upon animalcula, which are ever found to exist in water and 

 which they might separate from the constant stream, which they 

 pass from the posterior part of the shell, and which must be 

 taken in at another part. This interesting operation I witnessed 

 frequently in a vessel in which I kept them for some months. 

 If the water was not changed for twenty-four hours, I uni- 

 formly found my interesting captives perfectly quiet, but within 



* Regne Animal, vol. ii. p. 472. 



VOL. in. — 3 V 



