384 



MOLLUSCA. 



gmous or gelatinous common mass, and more or less constricted and dilated at particular parts*; but each orifice 

 always represents on the surface a little star with six rays. We unite them all under the name of Polyclinum. 

 Some cover foreign bodies like fleshy crusts ; others rise in conical or globose masses. Others again expand into 

 a disk, so as to have a distant resemblance to a flower or an Actinia ; or they are lengthened out into cylindrical 

 branches, supported by more slender pedicles; or they are grouped into cylinders (Synoieum, Lam.). It even 

 appears from some recent observations that the Escharidae, hitherto arranged with polypiferous Zoophytes, belong- 

 to the Molluscans of this family. 



THE FIFTH CLASS OF MOLLUSCA. 



THE BRACHIOPODES.f 



Like the Acephales, the Brachiopodes have a cloak with two lobes, anil this cloak is 

 always open. In place of a foot, they have two fleshy arms, garnished with numerous fila- 

 ments, which they can push beyond the shell and withdraw within it : the mouth is between 

 the insertions of the arms. We are not well acquainted with their organs of generation, nor 

 with the nervous system. J They are all covered with a fixed bivalve shell, and are conse- 

 quently destitute of locomotion. We only know three genera of them. 



The Lin'gul.e, Brug. — 

 Have two equal, flattisli, oblong valves, with the beaks at the end of one of the narrowest sides gaping 

 at the opposite end, and attached between the two beaks to a fleshy pedicle, by which they are sus- 

 pended to rocks. Their arms are rolled up spirally, to lie within the shell. It appears that their 

 branchiae consist of little leaflets, arranged all round each lobe of the cloak, on its internal surface. 



Only one species (Lingula anatina, Cuv.) is known, from the Indian Ocean. [Mr. Broderip has described two 

 other species.] 



The Terebratul^:, Brug. — 



Have two unequal valves united by a hinge : the summit of one, more protuberant than the other, is per- 

 forated to permit the passage of a fleshy pedicle which attaches the shell to rocks, madrepores, other shells, 

 &c. Internally, a small bony framework is observed, that is sometimes sufficiently complex, composed 

 of two branches, which articulate with the imperforate valve, and which support the two arms, edged 

 all round with long, closely-set fringes, between which there is, on the side next to the large valve, a 

 third simply membranous and much longer appendage, usually spirally convoluted, and fringed like the 

 arms. The mouth is a small vertical fissure between these three large appendages. The principal part 

 of the body, situated near the hinge, contains the numerous muscles, which reach from one valve to the 

 other, and between them are the viscera, which occupy but little space. The ovaria appear to be two 

 ramose productions, adherent to the parietes of each valve. I have not yet been able to satisfy 

 myself in regard to the position of the branchiae. Numberless Terebratulae are found, in a fossil or 

 petrified state, in certain secondary strata of ancient formations. The living species are less numerous. 



There are some species broader transversely, or longer in the direction perpendicular to the hinge, with a 

 margin entire, or emai ginate, or three-lobed, or with several lobes ; there are even some that are triangular : 

 their surface may be smooth, or furrowed, or veined : they are thick, or thin, or even transparent. In several, 

 instead of a hole in the apex of their valve, there is an emargination, and this is sometimes partly formed by two 

 accessory pieces, &c. It is probable that the animals, when better known, will present generic differences. Al- 

 ready there have been recognized in the 



Spirifer, Sow., two large cones, formed of a spiral thread, which appear to have been the supports of the animal. 

 In the Thecidea, Def., the support seems to have been incorporated with the small valve. 



The Orbicul^e, Cuv. — 

 Have two unequal valves, one of which, being round and conical, resembles the shell of a Patella : the 

 other is flat, and adherent to rocks. The arms of the animal (Crispus, Poli) are ciliated and spirally 

 curved, like those of the Lingula. 



* On these peculiarities Savigny lias fouiuled his genera Polychnum, 

 Aplidium, Ditlcmnum, Encaliiim, Viuzona, Sigilliua, &c, which 

 it appears to us unnecessary to preserve. 



t Palliotranvhiata of M. dc Blainville. [Rang makes them the 1st 

 order of the Testaceous Acephales.] 



J [Mr. Owen has an admirable memoir on their anatomy in the 1st 

 vol. of the Trans, of the Zoological Society.] 



§ Observations more precise than any we yet have made appear 

 necessary before we can arrange the Mtigns of Sowerby, the Strigoce- 

 phales of Defrance, and some other groups, near this one. 



