38 ANOMIADJE. 



ACEPHALA LAMELLIBRANCHIATA. 



ANOMIADJB. 



The only genus of this family, Anomia, is one of the Ostra- 

 ce& of Lamarck's monomyal order, which cannot be main- 

 tained in its integrity; zoologists have long removed the 

 Mytilidas from it to the Dimyte. It will be as well at once 

 to state, that all the monomyal animals of that eminent 

 naturalist are really Dimyae. It will probably create some 

 surprise when we say, that the only true Monomyce are the 

 Pholades and Teredines, as, we think, we have satisfactorily 

 demonstrated in their respective anatomies. All other bivalve 

 genera have two adductors; the anterior one in Anomia, 

 Pecten, and Ostrea is of so small a volume, as almost to have 

 escaped notice; and the great subcentral muscle in those 

 genera appears of a size as if the two ordinary dimyal ones 

 were amalgamated ; still the anterior adductor exists, and if 

 carefully searched for will be found under the beaks, pointed 

 out either by a single minute cicatrix, or by a little group of 

 five or six closely united, very small, muscular scars*; this dis- 

 position of the cicatrices varies in all the genera, so does the 

 main subcentral mass, as to shape and size. Careful dissec- 

 tions of the animals will show the muscular filaments adhering 

 to the circumscribed area under the beaks; but in oyster- 

 shells that have been exposed to the action of the sun and air, 

 and vicissitudes of weather, the minute anterior adductor is 

 perfectly visible. In the three genera we have mentioned, 

 these muscles are of small size ; they, however, in the next 

 family, the Mytilidte, though still small, have become more 

 developed, and in the following one of the Arcada they have 

 completely acquired the typical size and position, which is 

 maintained in all the remaining families, until they reach the 

 Pholadidte, when they merge into a single medial adductor, 

 both in the Pholades and Teredines. 



