332 
MOLLUSCA. 
Mollusca. is only one syphon and foot; in the third, a syphon and no 
\=-—~ feet; in the fourth there is an abdominal syphon and no feet; 
Cuvier. 
in the fifth there isa foot but no syphon; while, in the sixth, 
neither foot nor syphon can be discovered. In the forma- 
tion of his genera, Poli takes advantage of the various forms 
of the cloak and the branchiz. 
To the celebrated Cuvier, the conchologist is also under 
the greatest obligations. By applying his vast knowledge 
of anatomy to the examination of the molluscous animals, he 
has unfolded many new conformations of parts, and exhi- 
bited many unlooked-for relations. The vast collection of 
objects, the spoils of all the museums of the continent, which 
Paris once possessed, lay open to his inspection, and his in- 
dustry appears to have been equal to the harvest which in- 
vited him to labour. 
In his first attempts to classify the molluscous animals, as 
contained in his Tableau Elémentaire de [ Histoire Naturelle 
des Animauz (1798); and his Lecons @ Anatomie Comparée, 
(1800-1805), he employed chiefly the characters which the 
preceding writers had developed, in his inferior divisions ; 
but in his primary distinctions, he distributed the mollusca 
into three classes: Cephalopoda, having the head covered 
with tentacula, serving as feet; Gasteropoda, with the head 
free, the animal crawling on the belly; and Acephala, hav- 
ing no distinct head. 
Some years after the appearance of this classification, 
Cuvier directed more of his attention to the internal struc- 
ture of the mollusca, and, by means of accurate dissections, 
obtained a more intimate acquaintance with the organs and 
functions of these animals than any of his predecessors had 
acquired. The information which he thus gained was com- 
municated to the public at different periods, in the well- 
known publication Annales du Museum d’ Histoire Natu- 
relle de Paris. These papers, with some additional obser- 
vations, were at last published ina separate form, under the 
title Mémoires pour servir a Vhistoire et a V’ Anatomie des 
Mollusques, Paris,1816. In the following year he published 
Le Régne Animal, distribué @aprés son organisation, in 
which he arranged the mollusca according to his peculiar 
views, from characters drawn exclusively from the animal. 
In the third volume, of what may be termed the third edi- 
tion of that invaluable work, published in 1830, the same 
arrangement, with the exception of a few modifications, was 
adhered to. 
He divides the mollusca into six classes, which he terms 
Cephalopoda, Pteropoda, Gasteropoda, Acephala, Brachi- 
opoda, and Cirrhipoda. 
In the class CerpHaLopopa, the body is in the form of a 
sack, open above, containing the branchia, with a distinct 
head, surrounded by fleshy elongations or arms, adapted for 
moving the body or seizing prey. Into this class, along with 
the Sepia of Linnzeus, Cuvier has inserted the multilocular 
shells of his genus Nautilus and the genus Argonauta. But 
it is to be feared, that our knowledge of the testaceous mol- 
lusea which inhabit the numerous multilocular shells, is too 
limited to enable us to assign to all of them their true place 
in a natural arrangement of animals. 
In the second class, termed Preropopa, the body is 
closed, the head is destitute of the long fleshy arms which 
distinguish the animals of the preceding division; two fin- 
like membranes, situate on the sides of the neck, and on 
which the branchial tissue is in general spread, serve as or- 
gans of motion. ‘There is only one shelly mollusca belong- 
ing to this class, viz., the anomia tridentata of Forskaehl, 
now forming a part of the genus hyalea. 
The third class, which includes a great number of naked 
and testaceous mollusca, and to which Cuvier gives the name 
GasTeRoropa, from the circumstance of the belly being 
formed for crawling, has been subdivided into eight orders, 
from circumstances connected with the organs of respira- 
fon. 
In the first order, terméd Pudmones, which breathe air, Mollusca. 
he has constituted two divisions, the terrestrial and the aqua- "=" 
tic. The animals of the former live on land, and were in- 
cluded by Linnzeus in his genera limax and turbo. They 
are the land shells of most authors. Those of the division, 
termed aquatic, live in the water, but require at intervals to 
come to the surface to obtain fresh air. They constitute, 
with a few exceptions, the fresh water shells of naturalists. 
In the second and third orders, or Wudibranches and Infero- 
branches, the species consist almost entirely of genera formed 
from the animals which Linnaeus and many others included 
in the genus doris. They are naked mollusca, and are like- 
wise destitute of any internal testaceous plate. The fourth 
order, termed Tectibranches, contains animals whose branch- 
iz, like small leaves more or less divided, are situate on the 
right side, or upon the back. The animals of this division , 
possess a shell, but it is in general placed beneath the com- 
mon integuments, such as the genus Aplysia and several 
species of the genus Bulla. The fifth order, termed Heter- 
opodes, have the gills plumore and dorsal, with the foot 
compressed and vertical like a fin, with a small portion of 
it only formed to act as an organ of adhesion, as in the other 
gasteropoda. The Pectinibranches form the sixth order, 
and are distinguished by the branchie, which are like leaves 
or threads placed parallel in one, two, or three lines, on the 
surface of the pulmonary cavity, and by having the sexes 
separate. It includes the whole of the marine species of the 
Linnzan genera of turbinated univalves. Into this order, 
Cuvier, from the consideration of other characters, has in- 
serted the genus Cyclostoma, which, according to the cha- 
racters indicated by the respiratory organs, belongs to the 
Pulmones. 
In the seventh order, termed Scutébranches, the bran- 
chiz are similar to those of the preceding order, but the 
sexes are united, each individual being capable of impreg- 
nating or being impregnated. The shells in general are 
cup-shaped, and destitute of a lid. It includes the genus 
Halyotis, and many species of the old genus Patella. In 
the last order, called Cyclobranches, the branchiz appear in 
the form of small leaves or pyramids strung round the under 
margin of the cloak. They enjoy a hermaphroditism simi- 
lar to those of the preceding order. The species of the 
genus Patella which are allied to the vulgata, and the genus 
Chiton, are included in this order. 
In the fourth class, or ACEPHALA, he includes the bivalve 
shells, distributing them into families, from characters near- 
ly similar to those which we have pointed out as having 
been previously employed by Poli. 
The fifth class, termed Bracuropopa, contains animals, 
resembling those of the preceding class in having a cloak of 
two lobes, but these are always open. The branchiz con- 
sist of small leaves placed on the inner margin of each lobe. 
In place of a foot they have two retractile fleshy arms, 
which are extensile. This class includes the Patella unguis 
of Linnzus, the genus Terebratula and the Patella anomala 
of Miller. 
The class Crrrurpopa, distinguished by the articulated 
filaments with which the animals are furnished, contains the 
species of the genus Lepas of Linnzus. The shells belong- 
ing to the Linnean genera Sarpula and Dentalium, are 
transferred to the class termed Annelides. 
This system of the molluscous animals is unquestionably 
the most perfect of all those which have been published. 
But, with all its excellence, we must inform the reader, 
that many species, nay, whole genera, have their places as- . 
signed them in this natural method, merely because the 
shells occupied a similar position in the artificial system, the 
form of the inhabitants being unknown. 
Section 1V.—Mixed Systems. 
In this section, we shall confine our remarks to the only 
