ON MOLLUSCA. 147 
In the same year, 1757, Adanson, who grouped animals in 
families on no arbitrary system, but according as they exhi- 
bited the greatest number of relations among themselves, made 
a more extended application of these principles to the conchi- 
ferous mollusca, which he designates under the classific name 
of coquillages, in the first and only volume which he pub- 
lished of his Voyage to Senegal. He studies with care, dis- 
tinguishes, and denominates in a suitable manner, all the 
external parts, both of the animals and their shells. He then 
occupies himself in arranging those which he had observed in 
Senegal into a great number of systems, or tables of relation, 
considering, for instance, in the shell of the helix, the summit, 
the aperture, the opercle, the periosteum; in the conchs, the 
valves, according as they are equal or unequal, &c. 
Then passing to the animals, and always admitting his 
original division, into helices and conchiferous mollusca, he con- 
siders, in the first, the tentacula or horns, the eyes, their absence, 
existence, or situation in the head,the mouth, either with two 
jaws and without proboscis, or with proboscis and without 
jaws, &c. In the conchs he considers the mantle, the trachea, 
&c. He then describes and figures the species of shells, which 
he observed in Senegal. 
We may remark, that this work of Adanson’s, if not the first 
in which the principle of classification, by which the animal 
is regarded as well as the shell, is established, is at least that 
in which the means of applying this principle are to be found. 
It must be confessed, however, that Adanson has not always 
employed with success the excellent materials which he had 
prepared in so suitable a manner. In fact, the distinction of 
his genera is very far from being complete, especially in the 
conchifera: his approximations are not always very natural, 
in a variety of cases. To him, however, we are indebted for 
a knowledge of the numerous relations between pholas and 
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