acritous structure of the animals of the microscopical multilocular shells by M. Dujardin, in 1835;* and the third was the confirmation of Cuvier's opinion regarding the non-parasitism of the cephalopod found in the shell of the Argonaute. Hence, in 1836, we have, from the accomplished Professor Owen, the following improved and excellent method of the Cephalopoda:+

Order I. TETRABRANCHIATA. Branchiæ four in number. The Nautilus pompilius is the type of the order. Fam. 1. NAUTILIDE. Shell external; spiral or straight; septa smooth and simple, the last chamber the largest, and containing the animal: siphon central, or marginal and internal.-Ex. Nautilus, Clymenes, Campulites, Lituites, Orthoceratites. Fam. 2. AMMONITIDE. Shell external; spiral or straight; septa sinuous and with lobated margins, the last chamber the largest and lodging the animal: siphon central, or marginal and external.— Ex. Baculites, Hamites, Scaphites, Ammonites, Turrulites.

Order II. DIBRANCHIATA. Branchiæ two in number.

Tribe DECAPODA.

Fam. 1. SPIRULIDA. Shell partly internal; cylindri-
cal, multilocular, discoid, the whorls separated;
septa transverse, concave next the outlet, and with
regular intervals. Siphon marginal, and internal,
uninterrupted. Ex. Spirula.
Fam. 2. BELEMNITIDA. Shell internal, composed of
an external calcareous sheath, formed by a succes-
sion of hollow cones, the exterior being the largest ;
of an internal horny sheath, also of a conical form;
containing at its apex a chambered shell, the septa
of which are concave externally, and perforated by
a marginal and ventral siphon. Ex. Belemnites.
Fam. 3. SEPIADE. Animal, body oblong, depressed,
with two narrow lateral fins extending its whole
length. Shell internal, lodged in a sac in the back
part of the mantle, composed of an external cal-
careous apex or mucro, of a succession of calcareous
laminæ with intervening spaces filled with air, and
supported by columns, but not perforated by a
siphon, and an internal horny layer, corresponding

See the Annales des Sciences Naturelles for 1834 and 1835.
+ Cyclopædia of Anatomy and Physiology. Part vi., May, 1836.

to the anterior horny sheath of the Belemnites. Ex. Sepia.

Fam. 4. TEUTHIDE. Animal, body sometimes oblong
and depressed, generally elongated and cylindrical;
with a pair of fins varying in their relative size and
position, but generally broad, shorter than the body,
and terminal. Shell internal, rudimental, in the
form of a thin straight elongated horny lamina,
encysted in the substance of the dorsal aspect of
the mantle. Ex. Sepioteuthis, Loligo, Onycho-
teuthis, Rossia, Sepiola. ** Loligopsis, Cranchia.
Tribe OCTOpoda.

Fam. 5. TESTACEA. This family embraces the genus
Argonauta, and, perhaps, the fossil Bellerophon. It
is defined: Body oblong, rounded; mantle adhering
posteriorly to the head; first or dorsal pairs of arms,
dilated and membranous at the extremity: Funnel
without a valve, but articulated at its base by two
ball and socket joints to the inner sides of the mantle.
Branchial hearts with fleshy appendages: No in-
ternal horny or testaceous rudiments; but an ex-
ternal monothalamous symmetrical shell, containing,
but not attached to, the body of the animal; which
also deposits its eggs in the cavity of the shell.
Fam. 6. NUDA. Body generally rounded, mantle
broadly continuous with the back of the head.
Arms connected at the base by a broad web: first
pair elongated, and gradually narrowing to a point.
Funnel without an internal valve, or external joints;
branchial hearts without fleshy appendages; biliary
ducts without follicular appendages. Shell repre-
sented by two short rudimental styles encysted in
the dorsolateral parts of the mantle. Ex. Octopus,

Eledone.

2. PTEROPODA.

Mr. J. E. Gray has proposed to divide this small and curious class* into two orders: The first is called THECOSOMATA, because the body is enclosed in a thin shell. The head of the animals is indistinct, the mouth being placed in the centre of the two large wings, which are united into a

*M. Emile Blanchard's anatomy of the ganglia of the Pteropods confirms the view of Cuvier in making a separate class of them, in opposition to Blainville, who would mingle them with the Gasteropods.--Syst. Nerv. chez les Invertebres, 10.

funnel-shaped expansion; the gills are internal, and the creatures use their fins as oars to their boat-like shell when they swim on the calm ocean.

This order embraces four families: 1, CLEODORIDE, which have an elongate, or subglobose conical glassy shell; and the fins are simple without any intermediate foot-like lobe. 2, LIMACINIDE, distinguished from the first by its spiral discoidal shell. 3, CUVIERIDE, with a glassy conical cylindrical shell, which becomes truncate in its adult state and 4, CYMBULIADE, in which the shell is only of a firm gelatinous substance, variable in figure, but generally somewhat resembling a slipper.

The second order, or GYMNOSOMATA, are destitute of any shell; the head is distinct, and there are two or four distinct fins on the neck, and a central foot-like appendage between their bases. The gills are external. Three families enter into the composition of the order. The PNEUMODERMIDÆ have a fusiform body, and the head is furnished with two contractile arms, armed with peduncled suckers; they have two wings, and the gills are posterior. The CYMODOCEIDE have two wings on each side, placed in the space that separates the body into two parts; and the CLIONIDE have two wings only, which are said to be covered with a vascular network, and serve the purpose of gills. They and the Limacinæ are the chief food of the whales.*

3. GASTEROPODA.

The few alterations made by M. Rang in the arrangement of the Gasteropods, are in harmony with Cuvier's principles. His Nucleobranches, corresponding pretty exactly to the Heteropods of Cuvier, are placed at the head to make the alliance of the class with the Pteropods less abrupt; but it would have been better to have removed the Pteropods from the position they occupy to a lower rank; for we now know that their structure is of lower organization, and we know, moreover, that the pectinibranchial Gasteropods leave no space between them and the Tetrabranchiate Cephalopods to be occupied by any intervening class. The orders Pulmonés-opercules and Cirrhobranches were rejected by Cuvier, and with good reason: the former rested on characters incongruous with the system, and apparently of not more than subordinal value; and the structure of the Dentalium, the only cirrhobranchial Mollusk, seems to prove it to be a mere family *Syn. Brit. Mus. 1842, p. 86.

+ Blainville and Souleyet maintain that the Pteropods are a tribe of Gasteropods allied to Bulla and Aplysia.

group, situated between the Chiton and Patella. According to Deshayes, on whose authority the order Cirrhobranchiata solely rests, the branchiæ in Dentalium are grouped in the form of two tufts of long soft filaments with clavate extremities, one on each side of the animal's neck; but Mr. Clark appears to have proved that these organs are really salivary glands: so that the usually accepted view of the cirrho-branchiate character of Dentalium becomes unte

nable.*

In 1842, or earlier, Mr. J. E. Gray proposed a very material modification of Cuvier's arrangement; † and the differences between them will be made most obvious by reducing Mr. Gray's method to a tabular form. The Gasteropoda then areI. CTENOBRANCHIATA with the respiratory organs consisting of one or more comb-like gills placed on the inner side of the mantle, which forms an open bag in the last whorl of the shell, over the back of the neck. Order I. ZOOPHAGA, embracing five families, viz. — 1. Strombida; 2. Muricidæ ; 3. Buccinidæ ; 4. Volutida; 5. Cypræadæ.

Order II. PHYTOPHAGA.

Section I. Podophthalmi.

Eyes placed on short pedicels at the back inner angle of the tentacula.

* Sides of the body furnished with a fringe sending out a series of tentacular filaments.

The families are 1. Turbinidæ ; 2. Trochida; 3. Stomatellida; 4. Haliotida; 5. Fissurellida; 6. Dentaliada; 7. Lottiada.

**Sides of the body destitute of fringe and filaments. Tentacula generally elongate and slender. Shell interiorly always opake and porcellaneous.

The families are 1. Neritida; 2. Ampullariadæ ; 3. Ianthinida; 4. Atalantidæ.

Section II. Eriophthalmi.

Eyes sessile, or only placed on a very small prominence at the base of the tentacula: sides simple.

Branchiæ formed of triangular plates and not exposed: shells generally regularly spiral with a moderately sized aperture.

*Forbes and Hanley Brit. Mollusca, iii. 447. Mr. Clark's very interesting paper is in the Ann. and Mag. Nat. Hist. Ser. 2, iv. 321.

Synopsis of the Contents of the British Museum. Lond, 1842. Duod. -Mr. Gray states that his method was first published in 1838. Proceed. Zool. Soc. No. 178, p. 129.

The families are 1. Naticida; 2. Littorinida; 3. Truncatellida; 4. Paludinida; 5. Velutinidæ; 6. Pyramidellida; 7. Tornatellida. **Branchiæ formed of long filaments, and often protruded when the animal is expanded. Shell various and anomalous in form, with often a very large aper

ture.

The families are 1. Valvatidæ ; 2. Vermetidæ ; 3. Vanicoroide; 4. Capulida; 5. Crepidulidæ ; 6. Phoridæ. II. HETEROBRANCHIATA. Branchiæ variously formed, or respiring by means of lungs. Order III. PLEUROBRANCHIATA.

Branchiæ lamellar placed on the right side of the back, and covered with a thin mantle, which is sometimes protected by a small shell, more or less sunk within its substance. *Branchiæ on the side of the back and covered by the mantle.

The families are 1. Bullidæ; 2. Aplysiada; and perhaps, 3. Pterotracheidæ ; 4. Argonauta, and 5. Bellerophon.

** Branchiæ on the right side of the body, in the groove between the edge of the mantle and the foot.

The families are 1. Pleurobranchida; 2. Umbrellidæ. Order IV. GYMNOBRANCHIATA. Branchiæ naked, various, placed on different parts of the back, or a series of plates placed round the edge of the mantle.

*Branchiæ placed on the back and exposed.

The families are 1. Dorida; 2. Tritoniada; 3. Placobranchidæ.

** Branchiæ lamellar, on the edge of the under side of the mantle.

The families are 1. Phyllidiadæ; 2. Patellida; 3. Chitonidæ.

Order V. PNEUMOBRANCHIATA. Respiring free air. *The respiratory cavity closed by the edge of the mantle being attached to the back of the neck, leaving only a small hole, covered with a fleshy valve, for the entrance. and escape of air. No operculum.

A. Eyes on the top of the long cylindrical tentacula. The families are 1. Arionidæ; 2. Helicidæ; 3. Veronicellida; 4. Onchidiada.

B. Eyes placed at the base of the tentacula.

The families are 1. Auriculidæ; 2. Limnæadæ.

c. No distinct tentacula.

The families are 1. Amphibolida; 2. Siphonariadæ; 3. Gadiniadæ.