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Show 400 MOLLUSCA. the two valves, and lodging as many elastic ligaments; the irregular and foliaceous shell marked on the anterior side and under the hinge by a notch traversed by the byssus. The Pernc:e were also left by Linnc:eus amongj the Ostrec:e( 1 ). CnENATULA, Lam. The Crenatulc:e, lately separated from the Pernc:e, instead of hav. ing transverse cavities on a broad h.inge, are furnished with oval ones on the very margin, where they occupy but little of its breadth. The byssus seems to be wanting, and they are frequently found among sponges(2). It is thought that we may approximate to the Pernre, certain fos· sil shells, in which the hinge is also furnished with cavities more or less numerous, that correspond to each other, and thus appear to have furnished points of attachment to ligaments: thus those of the GERVILIA, Defr. Have a shell closely resembling that of the Volucellre, but with a kind of double hinge, externally with opposed cavities, receiving as many ligaments, and internally furnished with very oblique teeth in each valve. Their impressions are found along with Ammonites in compact limestone(3). The INoaERAMus, Sowet•b. Is remarkable for the elevation and inequality of the valves, the summit of which curves in a hook towards the hinge, and which has a lamella ted texture( 4 ). CAsTILLus, Brong. Independently of the depressions for the ligament, the Castilli are marked by a conical sulcus, sunk in a lip, which is bent at a right angle to form one of the margins of the shell. The valves are about (1) Ostrea isognomum, Chemn., VII, lix, 584;-0. perna, Jb., 580;-0. legumen, lb., 578;-0. epldppium, lb., lviii, 576;-0. mytiloi'des, Herm., Nat. llerl., Schr. II, ix, 9. (2) Ostrea picta, Gm., Chemn., VII, lvU.i, 575, or Crenatula phasionoptera, Lam., Encyc. Method., Test., pl. 2l6, f. 2;-Crenatula avicularis, Lam., Ann. du Mus, Ill, pl. ii, f. 3, 4;-Cr. mytiloi'des, Id., lb. f. 1 and 2. See also the great work on Egypt, Coq. pl. xii. (3) Gervilia solenoi'des, Defr., Blainv., Malac., lxi, 4.-G. pernoi'des, Deslon· champs, Soc. Lin. du Calvados, I, 116.-G. siliqua, Id. lb., &c. (4) Inoceramus concentricus, Parkins., Cuv. , Oss. Foss., 11, pl. vi, f. 11 ;Inocer. sulcatus, Id., lb., f. 12. ACEPHALA TEST A.CEA.. 401 equal, and of a fibrous texture. They appear to have had a byssus( 1 ). PuLVINITEs, Deft·. A regularly t~iangular .sh~ll, in which the few depressions diverge from the summit on the ms1de. The impression is found in chalk(2). In the second subdivision of the Ostracea, as well as in almost all the bivalves which follow, besides the single trans- , verse muscular mnss of the preceding genera, there is a fasciculus which is placed before the mouth, and extends from one valve to the other. It is apparently in this subdivision that we must place the ETHERIA, Lam. Large inequi valve shells, as irregular as those of the Ostrec:e, and more so; no teeth to the hinge; the ligament partly external and partly internal. They differ ft·om the Ostrec:e in having two muscular impressions. The animal is not seen to produce a byssus(3). They have lately been discovered in the Upper Nile( 4 ). ' A VICULA, Brug. · A~ equiva~ve shell with a rectilinear hinge, frequently extended into ~mgs by Its extremities, furnished with a narrow and elongated hgament, and sometimes with "small notches near the mouth of the animal; in the anterior side, a little beneath the angle of the side of the mouth, is a notch for the byssus. The anterior transverse muscle is excessively small. The species with less salient ears form the PINTADINJE, Lam., or MARGARIT.JE, Leach. The most celebrated, Mytilus margaritiferus, L., Chemn. V~II, lxxx, .717, 721, has nearly a semicircular shell, greenish Without, and ornamented with the most beautiful nacre within. The latter is employed in the arts, and it is from the extravasation of this substance that are produced the oriental or fine pearls, taken by the divers at Ceylon, in the Persian Gulf, &c. The name of AvwuLA is appropriated to such as have more (I) Catillus Cuvieri, Brong., Cuv., Oss. Foss., II, pl. iv, f. 10. (~) Pulvi~ites ~d~nsonii, Defr., Blainv., Malac., lxii, bis, 3. ~) Etherta elltpttca, Lam., Ann. du Mus. X, pl. xxix, and xxxi.;-Eth. trigo· ~~~3 'lb., pl. xx~;-Eth. seminularis, lb., pl. xxxii, f. 1, 2;-Eth. tran8Versa, lb., '· '4. (4) Eth. Caillaudi, Voy. de Caillaud a Meroe, II, pl. lxi, f. 2, 3. VoL. ll.-3 A |