244 SUPPLEMENT 
should that of the country, because neither furnish any cha- 
racters imprinted on the animal or on its shell. 
That of the nature of the aliment should not be admitted as 
of much more importance, because, though it is possible to 
conceive a certain correlation of visible organs with the 
structure of the digestive apparatus, more or less modified for 
a peculiar alimentary substance, yet such is never the case 
' with the mollusca. Accordingly we find species essentially 
carnivorous, as the testacelle, close by herbivorous species, 
like the limaces. 
The existence or absence of a protecting body is evidently 
of greater importance, since it is a character altogether ap- 
parent; nevertheless it is easy to see, though the number of 
exceptions be not very considerable, that in the same genus 
we may find conchyliferous species and others completely 
naked. 
The particular form of the body, the visceral part of which 
constitutes a wreath more or less elevated, is yet of less im- 
portance. 
The appendages, the lobes, the cirrhi which border the 
mantle, are of no greater import to consider, unless perhaps in 
the lamellibranches, in which the consideration of the tubular 
lobes, which prolong the mantle behind, present characters of 
real value. 
The distinction of the head from the rest of the body, as it 
is complete, incomplete, or non-existent, conducts to some 
divisions of the first order in the type of the malacozoaria, 
but it isa character not always sufficiently well marked. 
The number, the form,.the position of the tentacular ap- 
pendages which accompany the head, have perhaps some- 
thing still more constant, and consequently more essential to 
study, for the establishment of a classification in the mol- 
Jusca. We nevertheless occasionally find inexplicable ano- 
a 
