MOLLUSCA. 35 
His inferior divisions are destitute of precision, and the num- 
ber of species referred to limited. 
The system of D’Argenville, which was so much esteem- 
ed and so long followed in France, is essentially the same 
with that of Lister in the higher divisions. The plan is in- 
deed so simple, and in appearance so natural, that it has met 
with many admirers. It has even been useful in encourag- 
ing naturalists to study particular departments of the science, 
when they were prevented by their situation from devoting 
their attention to the whole. It is probably to this circum- 
stance that we are indebted to Schréter for his observations 
on the land shells in the neighbourhood of Thangelstadt. 
and on the river shells of Thuringia. 
The preceding arrangements, formed according to the 
situations in which the animals reside, and not according to 
their external coverings, may be considered as the first at- 
tempts at a natural method in conchology. They serve as 
an introduction to a new class of authors, whose views may 
be considered as of a higher order, and to whose labours we 
shall devote our attention in the following section. 
Secr. III.— Systems constructed from Circumstances con- 
necled mith the Form and Structure of the contained Ani- 
mal. 
The first attempt of any consequence to arrange testace- 
ous animals according to the soft parts of their bodies, was 
made by Adanson, in his Histoire Naturelle du Senegal, 
published at Paris in 1757. In this system, the ancient 
classes of Univalves, Bivalves, and Multivalves, are em- 
ployed under the titles des Limarons, les Conques, and les 
Conques Multivalves. 
