ON MOLLUSCA. 975 
are the ordinary bivalves, an innovation which, to a cer- 
tain point, has been adopted even by later writers. Not ad- 
mitting multivalves, he places the anatifee among the conchs, 
under the name of polyconche, while the balani form a divi- 
sion under the name of néduwli testacet. The bivalves are then 
divided according to the consideration of the resemblance or 
dissimilarity of the valves, and their more or less complete 
closure. He has, besides, proposed, rather than established, a 
great number of genera, which have since been adopted; but 
the characters which he assigns to them are so vague and so 
ill defined, that it is not wonderful that this writer should have 
remained in partial oblivion. 
We shall yet place before Linnzus, although the first 
editions of the Systema Nature had already appeared, the 
celebrated French traveller Adanson, because it appears 
almost indubitable, that it was from the latter’s “ Voyage to 
Senegal,” published in 1757, that Linneus has taken the most 
considerable part of his fixed general principles of conchology. 
Adanson, as we have already noticed in treating of the mol- 
lusca, took into consideration at once both the animal and the 
shell; he has nevertheless carried some innovations into con- 
chology, properly so called. Thus, beside a profound study of 
each of the parts of shells, and an exposition of the characters 
which may be drawn from them, he has, as it were, established 
upon each of them a particular system. He has, among other 
matters, divided the bivalve shells according to the number of 
the muscles, or of their attachments; and above all, he has 
introduced the consideration of the opercula, which before his 
time had been almost entirely neglected, or merely separately 
viewed under the name of marine wmbilici, without any refer- 
ence to the shells to which they had belonged. It was 
according to this character that he established, in the family 
of the helices, two sections, the first the univalve helices, and 
the second the operculated helices, which he considers as 
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