60 MOLLUSCA. 
attended to by naturalists. We do not here consider that 
character as of the highest kind, which is the most general, 
but that which has the greatest influence over the faculties 
and instincts of the animal. Had this subject been studied 
with greater care, the science of conchology would, at this 
period, have been in a more flourishing condition. To as- 
certain, in some degree, this subordination of character, is 
the object of the following observations. 
The division of the testaceous mollusca into three orders, 
as adopted by Linnezeus, is confessedly artificial. The Mul- 
tivalvia of that author possess no characters in common, nei- 
ther can they boast of a general resemblance. The first 
genus, Chiton, consists of animals which belong to the ce- 
phalous and gasteropodous mollusca. The animals of the 
genus Lepas approach more nearly to the crustacea than 
the mollusca ; while the animals, inhabiting the genus Pho- 
las, belong to the acephalous mollusca, and are closely con- 
nected with the Myze and Solenes. The shells of the first 
genus are merely calcareous scales, arranged transversely on 
the back of the animal. The shells of the second genus 
are variously articulated, fixed, and either sessile or pedun- 
culated. The shells of the third genus are bivalves, with a 
few accessory calcareous plates. It is to be hoped that mo- 
dern conchologists will avoid so incongruous a combination. 
The two remaining divisions of Linneeus, the bivalves 
and univalves, are not only obvious, but natural. They in- 
dicate the existence of certain forms peculiar to the animals 
whose shells are thus separated in the system. The uni- 
valve shells are inhabited by animals which possess a head, 
and whose organs of motion are either tentacula situated on 
the head, or a foot spread over the belly, as in the slug. 
The animals of the bivalve shells, on the other hand, are 
