MOLLUSCA. 331 
made by Adanson, in his Histoire Naturelle du Sénégal, Mollusca. 
Mollusea. That this sort of inquiry has in many instances been in- 
published at Paris in 1757. In this system, the ancient =~ 
Se —~ judiciously conducted, all who are acquainted with the sub- 
Systems 
founded on 
the habits 
of the ani- 
m 
al. 
Lister. 
S) 
D’ Argen- 
ibbald. 
ville. 
wm 
ystems. 
ject must admit. Due care has not been taken to distin- 
guish these minute testacea from the fry of the larger shells, 
so that the number of species has been very injudiciously 
multiplied. These remarks apply to several figures of 
Walker, and to a still greater number of those of Adams. 
Sect. II.— Systems constructed from Circumstances con- 
nected with the Habits of the Animal. 
The authors of the preceding class have laboured to bring 
to perfection the artificial system of conchology, and have 
formed their arbitrary characters, independent of the habits 
of life of the contained animal. But the naturalists whom 
we have now to consider, have traced these animals to their 
lurking places, and arranged them according to the situation 
in which they reside, instead of the forms which they ex- 
hibit. 
At the head of this class of conchologists, Dr. Martin Lis- 
ter stands pre-eminently conspicuous. His great work, en- 
titled Historia sive Synopsis Methodica Conchyliorum, was 
begun in 1685, and completed in 1692. It will long remain 
a monument of the extensive information and unwearied 
diligence of its author. The following synoptical view of 
the work will enable our readers to comprehend its plan; the 
original should be consulted with care. 
Lib. i. De Cochleis terrestribus. 
Pars 1. De Buccinis terrestribus. 
Pars 2. Cochlez nudz terrestres Limaces quibusdam 
dicte. 
Lib. ii. De Turbinibus et bivalvibus aque dulcis. 
Pars 1. De Turbinibus. 
Pars 2. De Testaceis bivalvibus fluviatilibus. 
Lib. iii. De Testaceis bivalvibus marinis. 
Pars 1. De Testaceis bivalvibus, imparibus testis. 
Pars 2. De Testaceis bivalvibus, paribus testis. 
Pars 3. De Testaceis multivalvibus. 
Lib.iv. De Buccinis marinis, quibus etiam vermiculi, den- 
talia et patella numerantur. 
The plan followed by Sir Robert Sibbald in his Scotia 
Iilustrata is somewhat different from that of Lister. He 
divides the Testacea into two classes, land and water shells, 
and the latter class he subdivides into fluviatile and marine. 
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 cireum- 
stance that we are indebted to Schroter 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. IIl—Systems constructed from Circumstances con~ 
nected with the Form and Structure of the contained 
Animal. 
The first attempt of any consequence to arrange testace- 
ous animals according to the soft parts of their bodies, was 
classes of Univalves, Bivalves, and Multivalves, are em-Adanson. 
ployed under the titles des Limacons, les Conques, and les 
Conques Multivalves. * 
Cuasse I. Les Limacons. 
Sect. I. Les Limacgons Univalves. 
Fam. 1. Les limacons univalves qui n’ont ni yeux ni 
cornes. ; 
Fam. 2. Les limac¢ons univalves qui ont deux cornes, et 
les yeux placés a leur racine et sur leur céte interne. 
Fam. 3. Les limacons univalves qui ont quatres cornes, 
dont les deux exterieurs portent Jes yeux sur le sommet. 
Fam. 4. Les limagons univalves, qui ont deux cornes et 
les yeux placés a leur racine, et sur le céte externe, ou pas 
derriére. 
Fam. 5. Les limacons univalves qui ont deux cornes et 
les yeux posés un peu au dessus de leur racine et sur leur 
cote externe. 
Sect. II. Les Limacons Operculés. 
Fam. 1. Limacons operculés qui ont deux cornes, avec un 
renflement, et qui portent les yeux ordinairement au dessus 
de leur racine, et 4 leur céte externe. i 
Fam. 2. Limacons operculés qui ont deux cornes sans 
renflement, et les yeux placés 4 leur racine, et sur leur céte 
externe. 
Fam. 3. Limacons operculés qui ont quatres cornes, dont 
les deux exterieurs portent les yeux sur leur sommet. 
CuasseE II. Les Conques Bivalves. 
Fam. 1. Les conques bivalves qui ont les deux lobes du 
manteaux separés dans tout leur contour. 
Fam. 2. Les conques bivalves dont les deux lobes du 
manteau forment trois ouvertures sans aucun tuyau. 
Fam. 3. Les conques bivalves dont les deux lobes du 
manteau forment trois ouvertures, dont deux prennent la 
figure d’un tuyau assez long. 
The presence or absence of an operculum or lid, gives 
rise, in this system, to a division of the univalves into two 
sections, and the families are established from circumstances 
connected with the number of the tentacula, and the num- 
ber and position of the eyes. The families amongst the bi- 
valves are arranged according to the structure of their cloak 
or external covering. In the class of multivalves, which 
we have omitted in the table, the characters are taken from 
the form and structure of the shell. 
The work of Geofiroy, entitled, Traité Sommaire des Co- Geoftioy. 
quilles tant fluviatiles que terrestres, qui se trouvent aux 
environs de Paris, 1767, is constructed upon the principles 
of Adanson. Here, however, the objects were not suffi- 
ciently numerous to admit of all the subdivisions of that 
author, but he has made the form of the animal subservient 
to the construction of generic characters. 
After these attempts. to classify the animals which inhabit Muller. 
shells had been made in France, the celebrated zoologist of 
Denmark, O. F. Miiller, turned his attention to the same 
subject. In the Zoologia Danica, which contains his di- 
gested views of the subject, he employs, in the construction 
of his genera of univalves, the characters first used by Adan- 
son; but among the bivalves, besides the form of the tubes 
or syphon, he notices the construction of the branchiz and 
the presence or absence of a foot. 
To our knowledge of the animals which inhabit bivalves, Po- Poli. 
li,m his expensive work, the History of the Shells of the Two 
Sicilies, made very importantadditions. Inthe construction of 
his families, which are six in number, he employs merely the 
characters furnished by the syphon and foot. In the first family 
the animal has two syphons and a foot; in the second, there 
