Lamarck has made Pecten and Lima the types of the Pecti- 

 nidae, and Ostrea that of the Ostreada ; so far we concur ; but 

 we must remove Anomia from the Ostreada, with which, 

 though it has the relations of the great subeentral muscle, 

 and absence of tubes, still there are closer ones, of a different 

 character, with the Palliobranchiata and the Pectinidce. 



Though the characters of the great subeentral or posterior 

 adductor muscle, the rudimentary, or no foot, and absence of 

 siphons, are very decided ones, and common to this particular 

 order or race, still it is not necessary that Anomia, Pecten, 

 and Ostrea should on those accounts form a single family, any 

 more than the Veneridae, Mactrida, and Cardiadcs, because 

 they have distinct tubes, foot, and are strict Dimyae therefore 

 these reasons, and those under each particular head, have 

 determined us to constitute Anomia, Pecten, and Ostrea as 

 distinct families. 



Anomia then, with its single species, constitutes the family of 

 theAnomiada, which we fix, according to our method, the first of 

 the Lamcllibranchiata, as it forms the decided point of passage 

 from the Palliobranchiata, by its constant state of fixture, by 

 a prolongation of the adductor muscle, through a perforation 

 of the valve, to marine substances, either by a ligamentous 

 or testaceous point of adherence; it also shows a similarity 

 in the disposition of the ovarium on the mantle, and posi- 

 tion of the animal in the shell. It will be observed that 

 in this statement there is not a single point of community 

 between Anomia and the Ostreada. Though Anomia, by the 

 small byssiferous foot, and the very singular doubled-up struc- 

 ture of the branchial laminse, shows a very intimate connection 

 with the Pectinidae ; nevertheless, from its constant fixity, the 

 perforated valve, ligamentous attachment, the texture of the 

 shell, its proteiform shape, and the hinge, it cannot, without 

 violence to established distinctions, be allocated with that 

 group. I think I have adduced sufficient reasons to support 

 the severance of Anomia from the Pectinidas and Ostreada 

 and I consider that there are equally good reasons for the 

 separation of Pecten and Ostrea. 



