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:-- 1. _Phyllidiana_ (plates, fig. 227 to 231), containing the genera Chiton, Chitonellus, and Patella, the two former of which present the only exception to the statement above made, that all the shells of Mollusca were univalve. 2. _Semiphyllidiana_ (plates, fig. 232 and 233). Of the two genera contained in this family, Pleurobranchus is broad, thin, and slightly spiral at the apex, and Umbrella is flat, circular, with a central apex. 3. _Calyptracea_ (plates, fig. 234 to 246). The patelliform shells of this family, although united by no other general characters, are brought together by the characters of the animals which produce them. The genera are Parmophorus, Emarginula, Siphonaria, Fissurella, Pileopsis, Calyptræa, Crepidula, Ancylus.