spiral, with a very wide and entire aperture: tentacula or none, or rudimentary, or earlike.

Family 1. SUBAPLYSIACEA. Two or four tentacular appendages: orifices of the generative organs approximate and without an intermediate furrow. Gen.: Barthella, Pleurobranchus, Pleurobranchidium.

Family 2. APLYSIACEA. Four tentacular earlike appendages sexual orifices distant and united by a furrow. Gen. : Aplysia, Dolabella, Bursatella, Notarchus, Elysia.

3. PATELLOIDEA. Body depressed and covered by a large external non-symmetrical_patelliform shell. Gen. Ombrella, Siphonaria, Tylodina.

4. AKERA. Body more or less globular, gasteropod, divided into two parts, the anterior often furnished with lateral lobes: head indistinct, without tentacula or with rudimentary tentacula. Ex. Bulla, Bullea.

SECTION II. Respiratory organs and shell (when it exists, which is rarely) symmetrical.

Order I. APOROBRANCHIATA. Body variable in form but always furnished with natatory appendages in pairs and lateral; no foot; organs of respiration often inconspi

cuous.

Family 1, THECOSOMATA.
dora, Cymbulia, Pyrgo.

Genera: Hyalæa, Cleo

2. GYMNOSOMATA. Genera: Clio, Pneumoderma.

3. PSILOSOMATA. Genus Phylliroe. Order II. POLYBRANCHIATA. Organs of respiration branchial, in numerous filaments or tufts disposed symmetrically and on the exterior of each side of the body, which is naked.

Family 1. TETRACERATA. Branchiæ simple, filamentous. Gen. Glaucus, Laniogerus, Tergipes, Cavolina, Eolida.

2. DICERATA. Branchiæ arbuscular. Gen. : Scyllæa, Tritonia, Thethys.

Order III. CYCLOBRANCHIATA. Organs of respiration branchial, more or less arbuscular, collected symmetrically near the vent which is on the median line of the posterior part of the body. Gen. : Doris, Onchidoris Peronia.

Order IV. INFEROBRANCHIATA.

Organs of respiration branchial, in the form of lamellæ under the projecting

margin of the cloak; body naked, oval, more or less tubercular.

Gen. Phyllidia, Linguella.

Order V. NUCLEOBRANCHIATA. Organs of respiration in the form of symmetrical filaments grouped with the digestive organs in a nucleus situated on the superior and, generally, the posterior part of the back; the skin thick, naked, and mucous. Shell symmetrical, more or less spiral longitudinally or from behind forwards, and very thin.

Family 1. NECTOPODA. A ventral foot compressed into a rounded swimmer. Gen. Pterotrachea, Carinaria.

2. PTEROPODA.

A winglike appendage on

each side of the body for swimming. Gen. : Atlanta, Spiratella, Argonauta.

Subclass III. P. HERMAPHRODITA.

Every individual of the species alike and unisexual. Shell simple, covering, rarely a little spiral, symmetrical or not, non-operculate.

SECTION I. Organs of respiration and shell symmetrical.

Order I. CIRRHOBRANCHIATA. Organs of respiration filamentous, scated on two sessile lobes above the neck. Gen. Dentalium.

Order II. CERVICOBRANCHIATA. Organs of respiration in a large cavity above the neck, with a wide opening in front.

Family I. RETIFERA. Organs of respiration retiform on the floor of the branchial cavity. Gen.: Patella.

2. BRANCHIFERA. Organs of respiration two large equal combs. Gen. FissureĤla, Emarginula, Parmaphorus.

:

SECTION II. Organs of respiration and shell non-symmetrical. Order III. SCUTIBRANCHIATA. Organs of respiration aqueous, and covered by a subspiral or patelliform shell. Family 1. OTIDEA. Respiratory organs on the left side. Gen. Haliotis, Ancylus.

2. CALYPTRACEA. Branchiæ above the origin of the back. Ex. Crepidula, Calyptræa, Capulus, Hipponyx.

Class III. ACEPHALOPHORA = Acephales, Cuv. Order I. PALLIOBRANCHIATA=Brachiopodes, Cuv.

N N

SECTION II. Shell non-symmetrical, irregular, attached.

Family 1. OSTRACEA. The Genera are Anomia, Placuna, Harpax, Ostrea, Gryphæa.

2. SUBOSTRACEA. Gen. Spondylus, Plicatula, Hinnites, Pecten, Pedum, Lima.

3. MARGARITACEA. Gen.: Vulsella, Malleus, Perna, Crenatula, Inoceramus, Catillus, Pulvinites, Gervillia, Avicula.

4. MYTILACEA. Gen.: Mytilus, Pinna. 5. POLYODONTA. Gen.: Arca, Pectunculus, Nucula.

6. SUBMYTILACEA. * Species with an epidermis, nacred, fluviatile. Anodonta, Unio.** Species without a distinct epidermis, not nacred, and more or less pectinate: marine.Cardita.

7. CAMACEA. *Shell irregular. Chama, Diceras, Etheria. **Shell regular. Tridacna, Isocardium, Trigonia.

8. CONCHACEA. Section 1. Regular with distant lateral teeth. Cardium, Donax, Tellina, Lucina, Cyclas, Cyprina Mactra, Erycina. Section 2. Regular without separate lateral teeth. Crassatella, Venus. Section 3. Irregular. Venerupis, Coralliophaga, Clotho, Corbula, Sphæna, Ungulina.

9. PYLORIDEA. Section 1. Ligament internal. Pandora, Anatina, Thracia, Mya, Lutricola. Section 2. Ligament external and swollen. Psammocola, Soletellina, Sanguinolaria, Solecurtus, Solen, Solemya, Panopæa, Glycimera, Saxicava, Byssomya, Rhomboides, Hiatella, Gastrochæna, Clavagella, Aspergillum.

10. ADESMACEA. Gen. Pholas, Teredina, Teredo, Fistulana, Septaria.

Order IV. HETEROBRANCHIATA=Acephales sans coquilles, Cuv.

Family 1. ASCIDIACEA = Ascidia, Lin.

Tribe 1. Simple Ascidia. Gen.: Ascidia, Bipapillaria, Fodia.

Tribe 2. Compound Ascidia.-Gen.: Pyura, Distoma, Botryllus, Synoicum.

2. SALPACEA.

Tribe 1. Simple. Gen.: Salpa.

Tribe 2. Compound. Gen. : Pyrosoma.

Sub-type. MALENTOZOARIA.

This division embraces two very dictinct classes. The first named NEMATOPODA is coequal with the genus Lepas of Linnæus, and the class Cirrhopodes of Cuvier; and as they are now considered to be constituents of the class Crustacea, I pass over their arrangement. The second class is named POLYPLAXIPHORA, and is instituted for the sole reception of the Chitons, multivalve shells with whose general appearance you are now familiar. The class, according to De Blainville, is very distinct from any other in the series of the animal kingdom, and apparently is the medium of transition from the cephalous mollusca to the Chetopodes,-an order in the Entomozoa or annulose worms. This opinion is founded on the kind of articulated shell which covers the back of the Chiton, and on the circumstance that the vent is not lateral and approximated to the mouth, as in other Mollusca, but perforated at the opposite extremity to the mouth, and in the median line, as it is in all Annelidans.

Incapacitated by his blindness, Lamarck had called upon M. Latreille to undertake his duty of delivering the lectures on the history of avertebrated animals at the Jardin du Roi; and the result was a system of the Mollusca by this great entomologist, in which the sexual peculiarities of the class assume the first rank, as if Latreille had imbued himself with the fancies of Oken concerning the predominancy of the sexual organs in the Mollusca. The system was published in 1825, a little before the appearance of Blainville's Manual, but subsequently to the publication of his classification in the "Dictionnaire des Sciences Naturelles." The following outline may give you some idea of it. Firstly the invertebrate animals are divided into the Cephalidiens and the Acephala. The Cephalidiens correspond to the

merely sentient or instincted animals of Lamarck, and embrace the molluscous and the conchiferous classes, which he proposes to call mantled animals-animalia penulata. The Molluscan race are divisible into two branches, the phanerogamous and the agamous or cryptogamic. The first copulate; the second have the sexual character masked and fecundate themselves. The phanerogamous are either finned or finless. There are two classes of the finned section, the CEPHALOPODS and PTEROPODS; and the finless are all GAS

TEROPODS.

The Cephalopods divide themselves into two orders. 1. the Decapods, with two families, one embracing the multilocular shells, and hence named Polythalama; the other named Enterostea, and represented by the genera Sepia and Loligo. The second order or Octopods has also two families,-a shelless one (Acochlides) for the Octopus; and one with its fine unilocular shell (Cymbicochlides), to receive the Ocythoc, Argonauta, and Bellerophon.

The class Pteropoda has two orders, Megapterygia and Micropterygia. In the first the swimmers are large. One family of them has a distinct head (Procephala), as instanced in Limacina and Clio; the other (Cryptocephala) has the head inconspicuous, with branchia separate from the swimmers; and the genus Hyalæa alone represents it. The second order has small swimmers, and the body has no shell; and a single genus, Pneumodermon, makes evident its insignificance.

The GASTEROPODA are either hermaphroditical or dicecious; and in both sections there are branchiferous and pulmonated mollusca. The order Nudibranchia introduces the first series, which seems to be connected with the Pteropods by the genus Carinaria, the first of the Nudibranches. These have three families named, from the position and form of the respiratory organs, Urobranchia, Seribranchia, and Phyllobranchia. This order is followed by that of the Inferobranchia, and this again by the Tectibranchia, of which one family (Tentaculata) has, and the other (Acera) has no tentacula. The order Pulmonea succeeds, and these are either naked (Nudilimaces), or terrestrial and cochleated (Geocochlides), or aquatic and shelled (Limnocochlides.)

There are only two orders of dioecious Gasteropods. The Pneumopoma, or operculated terrestrial mollusca, embraces the family Helicinides and Turbicina, each represented by a single genus. The Pectinibranchia is, on the contrary, a very extensive order with not less than eighteen families, divided into two very unequal sections according as the shell is ex