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Show 282 PISCES. ORDER II. CHONDROPTERYGII BRANCHIIS FIXIS, Or the Chondropterygii with fixed branchire, instead of having those organs free on the external edge, and opening all their intervals into a large common orifice, as is the case in all the fishes of which we have hitherto spoken, have them adhe· ring by this external edge in such a manner that they permit the water to escape through as, many holes pierced in the skin as there are intervals between them, or, at least, that these holes may terminate in a common duct, through which the water~ ejected. Another circumstance peculiar to these fishes is the presence of little cartilaginous bows, frequently suspended in the muscles opposite to the external edges of the branchire, and which may be termed branchial ribs. FAMILY I. SELACHII,-PLAGIOSTOMI, Dumer. This family, hitherto com prized under two genera, SQUALUS and RAIA, has many common characters. The palatines and post-mandibularies, alone armed with teeth, supply the place of jaws, the usual bones of which are reduced to mere vestiges; one single bone suspends these apparent jaws to the cranium, representing at once the tympanal, jugal and tempo· ral bones, and the preoperculum. The hyoid bone is attached to the single pedicle just mentioned, and supports branchios· tegal rays, as in ordinary fishes, although they are not so very visible, externally; it is followed by the branchial arches, as usual, but neither of the three pieces compose the operculum. These fishes have both pectorals and ventrals: the latter are are situated behind the abdomen, and on each side of the anus. Their membranous labyrinth is enclosed by the cartilaginous substance of the cranium; the sac, which constitutes part of it, CJIONDROPTERYGII llRANCHIIS FIXIS. 283 contains mere amylaceous masses, and not stones. The pancreas resembles a conglomerated gland, and is not divided into distinct tubes or creca. The intestinal canal is short in proportion, but a portion of it is provided internally with a spiral lamina, which retards the expulsion of the aliment. Fecundation is performed by an intromission of semen; the females have highly organized oviducts, which supply the place of a matrix in those whose young are hatched within their body; the others produce ova, invested with a hard or horny shell, to the formation of which a large gland that surrounds each oviduct contributes. The males are recognized by certain appendages, situated on the internal edge of the ventrals, which are very large, and highly complicated, and whose use is not well understood. SQUALus, Lin.(l) The Sharks form a first great genus distinguished by an elongated body, a thick fleshy tail and moderate pectorals, so that the general figure approaches that of ordinary fishes; the branchial openings correspond with the sides of the neck, and not with the under surface of the body as we shall see is the case with the Rays; the eyes also are on the sides of the head. The snout is supported by three cartilaginous branches connected with the anteriot· part of the Cl'anium, and the rudiments of the maxillaries, intermaxillaries, and premandibularies are evident in the skeleton. The shoulder bones are suspended in the muscles behind the branchire without articulating either with the cranium or spine. Several are viviparous. The others produce ova invested with a yellow and transparent horn, the angles of which are prolonged into horny cords. The little branchial ribs are apparent, and there are also small ones along the sides of the spine, which is co~pletely divided into vertebrc:e. The genus is very numerous and authorizes various subdivisions. We first separate the SoYLLiuM, Cuv.(2) Distinguished from other Squali by the shot·t and obtuse snout, (1) Squalus, the Latin name of a fish, employed by some authors; the species, however, is unknown. Artedi applied it to this genus. We also find 8qualua for Sqwiina. (2) &yllium, one of the Greek names of this fish. \ |
