MOLLUSCA. O9 



forms these shells into two sections, the first containing 

 those shells which have the muscular impressions separate 

 and lateral, and the second such as have only one subcen- 

 tral, simple, or compound impression. However highly we 

 respect the conchological labours of this naturalist, we can- 

 not join with him in the present instance, and elevate a sub- 

 ordinate character to a primary rank. If, by muscular im- 

 pressions, he means those marks impressed on the valves of 

 the shells by the muscles which serve to close it, then his 

 character is unconnected with any of the primary functions 

 of the inhabitant. For is it of much consequence whether 

 the valves be brought into contact by the action of one 

 muscle or by the assistance of two ? In so far, the charac- 

 ter is evidently artificial, when the impressions of the ab- 

 ductor muscles only are employed. But he evidently uses 

 the term in a more extensive sense, to refer to those im- 

 pressions left on the shell by some of the other muscles by 

 which the animal is attached to it. To the mere concho- 

 logist, these marks are of a very uncertain import, and 

 can never enable him to construct natural families, and the 

 student of the mollusca will employ more important distinc- 

 tions. If we are to take all the muscular impressions into 

 account, the arrangement of Lamark must undergo great 

 alterations. Let us take the common mussel as an exam- 

 ple. It is placed by the French Conchologist in the second 

 section, as having only one muscular impression, although 

 no less than four muscles adhere to each valve, destined for 

 the performance of very different functions. The largest 

 impression, which is situate near the obtuse end of the 

 shell and towards the posterior margin, belongs to the ab- 

 ductor muscle, employed in closing the valves. Connected 



