232 Mr C. Collier on Univalves. 



The perforated disc was closed within by the lining membrane 

 of the shell, and by that mass which has been alluded to as the 

 foot. There were no tentacula observed by me, and none, cer- 

 tainly, passing through the perforations. The mouth was 

 fleshy, and the oesophagus to be traced into a soft black mass, 

 which formed the greater part of the animal. Beyond these 

 facts, from the exceeding difficulty experienced in the examina- 

 tion, I hesitate to speak. The membrane passed to the open 

 extremity, and it there contained fluid ; it resembled an air-ve- 

 sicle of fishes. 



Were it not decided by the high authority of M. Cuvier, I 

 .should have concluded, from my opportunity of observation, 

 that the circulating system was the same as in mollusca. The 

 muscular system of both these species was of a very pale white, 

 and the red muscles of the mouth less florid than in that class. 



This brief review of the features of mollusca shews them to 

 be often diff^erent among individuals of the same family, consi- 

 dered as to the form of the shell, and to be always so inter- 

 mingled as not to afford generic distinctions. 



The annexed table displays the assemblage of organs in the 

 different families ; and, on consideration of the facts, it seems 

 impossible to select generic features capable of being discrimina- 

 ted and cognizable in a system*. 



If the inference be granted, it follows that the shell must be 

 considered alone ; and it is to be regretted that so able a natu- 

 ralist as Linnaeus did not transfer to this science the principles 

 of arrangement and nomenclature which he adopted so success- 

 fully in botany. To facilitate the acquisition of knowledge in 

 any branch of natural history, the generic name ought to desig- 

 nate the part or condition in which the distinction as a family 

 rests ; and this part or condition ought to exist through all the 

 individuals. The intention of all system is to arrange and to 

 generalize isolated facts, so that, by abstraction of what is par- 

 ticular, one family may be separated from another of the same 

 order, and the order, in its turn, from another of the same 

 class. 



What applicability is there in any one of the terms now em- 



• This table was wanting in the accompanying MS.— Edzt. 



