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Show 318 MOLLUSCA. If the whorls do not envelope each other, they are the HEuoos. TEGA AMMO NO IDA( 1 ). If the whorls are elevated as in most Univalves, they are the HE· LIOOSTEGA TURBINOIDA(2). Simple cells may also be strung upon a single, straight or slightly curved axis constituting the family of the 8TYOOSTEGA(3). ' . . Or they may be arranged m two alternate ser1es, when they be. come the ENALLOSTEGA( 4). VERTEBRALINA, CiSSIDULINAo ( 1) M. D'Orbigny divides them into four genera: SoLDANIA, 0l'ERCULINA1 PLANORBULIN A1 PLANULINA. (2) These form ten genera; TRUNCATULINA, GYnoiDINi, GLOBIG:ERINA, C . u,cAniNA, where is placed, among others, the Nautilus Spengleri, Fich. and Moll., XIV, d., I, and XV. RoT ALIA, RosALINA, VALVULINA, BuLJJ\IINA, UviGERINA, CLAVULJNA. (3) The Stycostega are divided by M.. D'Orbigny into 'eight genera: the Nono· unu, which he subdivides into the true Nonounu, such as the Nautilm radicu· lus, L.;-Naut.jugorus, Montag., Test. llrit.,XIV, f. 4; and into DENTALINA, such as the Nautilus rectus, Montag., I, cit., XIX, f. 4, 7 (the genus R:&ol'HAGA, ?tfontf., I, 330); into OnTHOC:ERINA, such as the Nodosaria clawlus, Lam., Encycl., pl. 466, f. 3; and into MucnoNINA, FRoNDICULAnu, where comes Renulina complanata, Blainv., Malac. LINGULIN.~, RIMULINA, VAGINULJNA, to which belongs tbe Nautiluslegume.n, Gm., Plane., I, f. 7; En· cy., pl. 465, f. 3. MAnGINULINA, where we find tbe Nautilus raphanus, Gm., Soldan., II, xciv. PLANULARIA, such as the Nautilus crepidulu1, Fich., and Moll., XIX, g, h,i. PAVONINA. (4) M. D'Ot·bigny has five genera of Enallostegae: BIGENERINA, • TEXTULARIA, VULVULINA1 DrMORPRINA, PoLYMORPHJNi, CEPHALOPODA. 319 Or a few of them may be collected and united as in a pellet, forming the AGATHISTEGA( 1 ). Finally, in the ENTOMOSTEGA(2) the cells are not simple as in the other families, but are subdivided by transverse septa in such a way that a section of the shell exhibits a sort of trellis. VntGULINA, SlBEROIDINA. (1) The .!lgathi8tega or Milliola of authors, which compose immense banks of calcareous stone, in the arrangementofM. D'Orbigny, only form sixgenera: BILOOULINA, SliB.OLOCULINA, TBILOCULINA, ABTICULilU, QUilfQ.UELOCULIN-'.1 ADELOSINA. M· de Blain ville assures us that he has ascertained, from observation, that their animal has no tentacula: should this be the case, they are at once greatly removed from the Cephalopoda. (2) The Entomostega resemble, externally, several of the Helicostega. M. D'Orb. divides them into five genera: AnsxsTEG YN A, HETEROSTEG YN A1 0B.BICULINA, ALVEOLINA, FUULARU.. Those who are desirous of penetrating more deeply into the study of this curious portion ofConcbyliology, on which our limits forbid us to expatiate, but which may be useful in the investigation of fossil strata, will find an excellent guide in the Table Method. des Cephalopodes, inserted by M. D'Orbigny in the Ann. des Sc. Nat.,1826, tome VII, p. 95 and 245, and may profit by tbe large models constructed by this able observer. \ |