1st Sub-order, Cuv.
1st Pam. Phyllidia, fig. 175.
2(1 Sub-order, Semi-phyllidiade, Lam.
2d ram. Gastraplar, Blainville.
3d Fam. Pleurobranehus, Cuv.
Order III. TECTIB RA NCH IA TA ,* (Cuv.) Syn. Chismobranches, Blainville; Gast. Adelabranehes,t Dumeril; Gast. Phyllidiens and Laplysiens, Lamarck.
In this order the branchime are placed upon the dorsal aspect of the body, but are pro tected by a fold of the mantle which almost always contains a shell presenting a rudimen tary spire. They are all hermaphrodite like the preceding, and marine.
1st Fam. Dikera.
2d Fam. Akera.
Order IV. PULMONALIA CULATA, (Ferussac ) Syn. Pulmones, Cuv.;1 Pulmobranches, Blainville ; Gast. Traehelipodes,§ Lamarck.
The respiratory apparatus is here adapted to the respiration of atmospheric air, and instead of being composed of branchial tufts or la mina?, consists of a cavity lined by the rami fications of the pulmonary vessels, the entrance to which can be opened or closed at the plea sure of the animal. Almost all the species are provided with a shell either turbinated or concealed within the mantle, but are never furnished with a calcareous operculum. Every individual is hermaphrodite, hut mutual copu lation is essential to fertility. Some are terres trial, others inhabit fresh water, and some are marine.
1st Sub-order, Geophilicle,* Ferussac.
1st Pam. Limas.
2d Farm Helic.
2d Sub-order, Gchydrophilide,t Ferussac. 3d Fam. Auricula.
3d Sub-order, Ilygrophilide,1 Ferussac. 4th Fam. Litnneus.
Order V. PUIAIONALIA LATA, (Ferussac.) Syn. Peetinibranehiata,§ Cuv. ; Siphoni branehiata,11 The respiratory organs of the animals form ing this order are similar in structure to those found in the last, but they differ materially in other points. In all the operculated division the shell is closed by a calcareous operculum not found in the last, and instead of that hermaphrodite condition of the sexual organs common to the inoperculated order, the sexes are distinct, the male and female parts existing in different individuals. They are all terres
trial.
1st Fam. Helicina.
2d Pam. Turbieina.
Order VI. PECTIN1BRANCHI.ATA, (Cuv.) Syn. Trachelipodes, Lamarck ; Monapleuri branches, Blain.; Gast. Adelabranches and Siphonibranches, Dumeril.
This extensive order, which comprises most of the univalve mollusks whose shells enrich our cabinets, is characterized by a respira tory apparatus adapted to an aquatic medium. The branchim are pectinated, consisting of ranges of fringes disposed like the teeth of a comb, and generally enclosed in a dorsal cavity which opens externally at the side of the body or above the head. The shell is always turbi nated, and sometimes provided with an oper culum. The sexes are separate, and the ani mals fluviatile or marine.
1st Sub-order, Pomastomidee,11Ferussac ; Chis mobranches, Blainville.
1st Fam. Turbo, Lin.
2d Fam. Trochus, Lin.
2d Sub-order, Hemipomastamide, Ferussac. 3d Fam. Cerithbon, Adanson.
4th Fam. Buceinum, Lin.
5th Fain. Murex, Lin.
6th Fam. Strombus, Lin.
7th Fain. Cosmos, Lin.
3d Sub-order, Apomastomide, Ferussac. 8th Fatn.
9th Pam. TToluta, Lin.
10th Pam.
4th Sub-order, Adelodermide, Ferussac. 11 th Fam. Sigaret us, Order VII. SCU2'113RANCHIATA,• (Cuv.) Syn. Cervicobranches, Blain. ; Chismobraaches, Blain.; Gust. Dermobranches, Dum.; G. Trachclipodes, Lam.
In this order the structure of the branchiw is analogous to what has been described in the Pcctinibranchiata; but the shell, which in the latter was always turbinated, in the Scutibran chiata is a mere shield, in which the indications of a spire are very slight or totally deficient. There is never an operculum. The organs of both sexes are united in every individual, but there is no necessity for copulation, each ani mal being self-impregnating. The species are all aquatic.
1st Sub-order, Anthophora.t 1st Fain. Haliotis, fig. 176.
2d Sub-order, Calypiracid•a Lam.
2d Fam. Captain.• 3d Sub-order, licteropodat Nucleobranches, Blainville.
3d Fam. Pterotracheu, fig. 177.