1. Tubicolæ (plates, fig. 44 to 54), having shelly tubes besides the valves. This family contains the genera Aspergillum, Clavagella, Teredina, Teredo, Xylophaga, Fistulana, and Gastrochæna.
2. Pholadaria (plates, fig. 55 to 59), cylindrical, living in holes in rocks pierced by the animals. Lamarck places in this family the genera Pholas and Gastrochæna, the last of which belongs more properly to the family Tubicolæ, as placed above.
3. Solenacea (plates, fig. 60 to 68), longitudinally (transversely, Lam.) elongated, open at the anterior and posterior extremities. This family contains the genera Solen, Pholadomya, Panopæa, Glycimeris (Solecurtus) and Solenimya.
4. Myaria (plates, fig. 69 to 76), ligament internal. A spoon-shaped ligamentary pit in one or both valves. Shell generally gaping at one or both extremities. This family includes the genera Anatina, Mya, Anatinella, Lyonsia, Myochama, Cleidotherus.
5. Mactracea (plates, fig. 77 to 88), the cartilage placed in a trigonal pit, with a small external ligament. The genera Lutraria, Mactra, Crassatella, Erycina, Ungulina, Amphidesma, and Solenimya belong to this family, the last of which ought to have been placed among the Solenacea, as above.
6. Corbulacea (plates, fig. 89, 90), inequivalve, with an internal ligament resembling the Mactracea, but differing in having one valve deeper than the other, although regular shells. This small family contains only the genera Corbula and Pandora.
7. Lithophagidæ (plates, fig. 91 to 97), irregular, terebrating, living in holes of rocks. The genera are Saxicava, Petricola, and Venerirupis.
8. Nymphacea (plates, fig. 98 to 110), ligament external, generally placed upon a prominent fulcrum, which passes from the inside to the outside of the hinge; valves generally gaping at the extremities. This family contains the genera Sanguinolaria, Psammobia, Psammotæa, Tellinides, Corbis, Lucina, Donax, Capsa, and Crassina.
9. Conchacea (plates, fig. 111 to 121), regular, having several cardinal teeth and sometimes lateral teeth. The Conchacea constitute one of the most beautiful and numerous families of the class; they present equivalve shells, which are always regular, unattached, and in general closed, especially at the sides; they are always more or less inequilateral. They are divided into the fluviatile and marine Conchacea, the first containing the genera Cyclas, Cyrena, and Galathæa, found in rivers; and the second, Cyprina, Cytherea, Venus, and Venericardia.
10. Cardiacea (plates, fig. 122 to 130). This family, which resembles the last in some general characters, are also regular and equivalve, and are generally provided with radiating ribs, which are seldom seen in the Conchacea. The genera enumerated in this family are Cardium, Cardita, Cypricardia, Hiatella, and Isocardia.
11. Arcacea (plates, fig. 131 to 138). These are known by having a row of numerous small teeth on the cardinal hinge in each valve. The genera included are, Cucullæa, Arca, Pectunculus, Nucula.
12. Trigonacea (plates, fig. 139 and 140). It is doubtful whether this family should remain distinct. As of the two genera placed in it, the first, Trigonia, is thought by some naturalists to have strong affinities with Nucula, in the family of Arcacea; and the latter, Castalia, certainly belongs to the Nayades.
13. Nayades (plates, fig. 141 to 152). These are fresh-water shells, covered on the outside by a thick horny epidermis, and pearly within. They include the genera Unio, Hyria, Anodon, Iridina.
14. Chamacea (plates, fig. 153 to 155), inequivalve, irregular, foliaceous, attached; containing the genera Diceras, Chama, and Etheria.
Second Order, Conchifera Monomyaria.
Having one adductor muscle, and therefore only one impression in each valve. They are separated into the following families:—
1. Tridacnacea (plates, fig. 156 & 157), transverse, equivalve, with an elongated muscular impression, near the centre of the ventral margin; margin undulated at the termination of the radiated large ribs. The genera Tridacna and Hippopus are included.
2. Mytilacea (plates, fig. 158 to 162), generally regular, with the hinge linear, without teeth, occupying the greater part of the dorsal margin. This family includes the genera Modiola, Mytilus, Pinna.
3. Malleacea (plates, fig. 163 to 170), shell generally thin, inequivalve, irregular, foliaceous, with the hinge linear. This family contains the genera Crenatula, Perna, Malleus, Avicula, Meleagrina.
4. Pectinides (plates, fig. 171 to 178). The Pectinides are generally regular or nearly so, with the shell solid; the greater part of them are auriculated at the dorsal margin, and generally characterized by ribs radiating from the umbones. The genera are Pedum, Lima, Plagiostoma, Pecten, Plicatula, Spondylus, Podopsis.
5. Ostracea (plates, fig. 180 to 192). The shells of this family are irregular, generally attached and foliaceous. They compose the genera Gryphæa, Ostræa, Vulsella, Placuna, Anomia.
6. Rudistes (plates 193 to 200). This family is composed of a particular association of shells, which appear on one side to be connected with the Ostracea; and on the other to approach the Brachiopoda. They differ from Ostracea in having no hinge or ligament, and only resemble them in their irregularity and foliaceous structure. The following six genera are placed by Lamarck in this family:—Sphærulites, Radiolites, Calceola, Birostrites, Discina, Crania. Of these, Calceola, Discina, and Crania are shewn to belong to the Brachiopoda.
7. Brachiopoda (plates, fig. 201 to 219). The shells of this family are inequivalve, equilateral, and attached to marine bodies by a tendon passing through one of the valves. The animals have, near their mouth, two elongated, ciliated arms, which are spirally rolled when at rest. The following genera are enumerated by Lamarck, Orbicula, Terebratula, Lingula.
MOLLUSCA.
Lamarck applies, or rather restricts, this name to those invertebrated animals, which while they are inarticulate in all their parts, have the head sufficiently advanced at the anterior part of the body to be distinguished; which is not the case with the Conchifera. All the shells are univalve, and are divided into six orders, namely, the Pteropoda, which have wing-shaped natatory organs or fins, and have light, thin transparent, nearly symmetrical shells; the Gasteropoda, with the foot not distinguishable from the rest of the body, have patelliform, open, and scarcely spiral shells; the Trachelipoda with the foot distinct and attached to the neck of the animal, have spiral, non-symmetrical shells. The Cephalopoda, with arms covered by suckers surrounding the head of the animal, have generally symmetrical convolute shells. The Cephalopoda are divided into C. polythalamia, which have the internal cavity divided into chambers by septa, as in the Nautilus; and the C. Monothalamia, which are not so divided, as the Argonauta. The order Heteropoda contains the genus Carinaria alone.
Order Pteropoda.
This order, containing hyaline, symmetrical, non-spiral shells, as above described, is not divided into families, but contains the following genera, Hyalæa, Cleodora, Limacina, Cymbulia; the first of which, although composed of a single piece, resembles a bivalve so nearly, that Linnæus actually placed it in his genus Anomia.
Order Gasteropoda.
With the exception of the genus Bulla and Vitrina, the last of which forms a passage into the next order, the shells contained in this order are patelliform, open, and scarcely spiral. They are divided into the following families:—