384 MOLLUSCA. 



glno^^^ or f^elatinous common niaijs, and more or less consti'ictcd and dilated at particular parts*; l.mt each orifice 

 ahvays represents on tlie surface a little star ^vith six rays. We unite them all under the name q{ Polydinum. 

 Soiue cover fi.irei^^n bodies like fleshy crusts ; others rise in conical or ijlobuse masses. (Jthers a;i;ain expand into 

 a ili.^k, so a^i tu ba\r a distant resemblance to a liower or an xVctinia; or they are len;i"thened out into c> lindi'icid 

 branclK-s, siipporti'd by more slender pedicles; oi" tbey are ufroiiped into cylinders {.S'//Ho/Vj/m, Lam.). It even 

 appears from some recent observations tliat the Escliaiida', hitherto arrang-ed uitb polypiferous Zoophytes, belon;^ 

 to the Molluscans of this family. 



THE FIFTH CLASS OF MOLLUSCA. 



THE BRACIIIOPODES.f 



Like the Aeepbales, tlie Cracliiopodes have a eloak with two lobes, and this chjak is 

 ahvays ojieu. In jilace of a foot, they liaAe t\vo tleshy anus, g;arnishe(l with numerous tila- 

 uients, which tht'v can push beyond the shell and withdraw within it: the mouth is between 

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

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

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



The Lingul.e, Brag. — 

 Have two equal, flaltish, ohlong valves, with the beaks at the end of one of the narrowest sides gaping 

 at the o]iposite 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 

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



Only one species (Liih/ula aiialina, Cmv.) 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 iicrniitthu passage of a fleshy pedicle wdiich attaches the shell to rocks, madrepores, other shells, 

 (ic. 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 convoluteil, and fringed like the 

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

 of the liody, situatcil near the hinge, contains the nunici'ous muscles, which reach from one valve to the 

 other, and betucen them are the viscera, \Nhicli occupy Ijut little space. The ovaria appear to be twu 

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

 mvsclf in regard to the position of the branchiae. Numberless Tcrebratulffi are foaml, in a fossil or 

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



There are some species broader transversely, or lonj^cr in the direction perpendicular to tlie hintje, with a 

 margin entire, or emarginate, or three-lobed, or with se\'eral lobes; there are even some that are trian;,'-ular : 

 their surface maybe smooth, or furrowed, or reined: they are thick, or thin, or even transpaient. In several, 

 instead of a hole in the apex of their valve, there is an eniarg:ination, and this is sometimes partly formed by t\\o 

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

 ready there have been recognized in the 



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

 In the Thfciilca, Def., the suppnrt seems to have been incorporated with the small valve. 



The Orbicul^, Cuv. — 

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

 other is Hat, and adherent to rocks. The arms of the animal {Crispus, Poh) are ciliated and spirally 

 curved, like those of the Lingula. 



•■ Oii these- poculiafillcsSftvJ)rny lias fmiJicletl hli^ \ic<\er^ Pofi/cl in n»i, J [Mr. 0m-uii Iias an mlmirable memoir on their auatoiny iii the Isl 



^piidiian, JH.t^mnuui, Eucieliiim, JJiitzona, Si/^iUinii, &c.. which vol. u( ihe Trxnt. of llic yAmlof^'irnl Socic/r/.] 

 it appears 10 us uiiiiei 

 t i^dtiobi-'na-hiul, 

 (irrk-r of thi; Test^ieoi 



