File:Text book of zoology (1896) (20714332752).jpg

Title: Text book of zoology
Identifier: cu31924000397905 (find matches)
Year: 1896 (1890s)
Authors: Boas, J. E. V. (Johan Erik Vesti), 1855-1935; Boas, J. E. V. (Johan Erik Vesti), 1855-1935. Lehrbuch der Zoologie
Subjects: Zoology
Publisher: London, Sampson Low, Marston
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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384 Vertebrata. some of the remaining placoid scales form large spines; and that the buccal teeth are low knobs (sometimes pointed) or plates, which are aiTanged in several rows and form a mosaic over the edges of the jaws. In general appearance, therefore, the Skates differ considerably from the Sharks. The skate type is not always developed to the same extent; in some forms the pectoral fins are smaller, the tail more powerful; whilst, on the other hand, there are Sharks (Squatina, the Sea- angel), which are somewhat flattened, with the eyes turned upwards, and large horizontal pectoral fins reaching antero-posteriorly along the sides of the head, but not attached to it. There is indeed a complete series of transitional forms, between the usually slim shark type, to the most extreme ray type with its discoid shape, wider than it is long, and with its thin caudal whip. In British seas there are several species (chiefly of the genus Baja), all typical Rays. Of forms belonging to the Southern seas may be mentioned the Electric Skates (Torpedo), and the Saw-fish (Fristis); the former are well known on account of their powerful electric organs, which lie on either side of the head; in the Sawfish the snout is drawn out into a long, straight, naiTOw plate, with a series of large, laterally directed, teeth on each edge. Both the Electric Skates and the Saw-fish, but especially the latter, belong to the more shark-like Rays, with toler- ably powerful tail. Both genera occur in the Mediterranean. 3. The Cat-fishes (Holocephali) genus Chimssra, etc., form a small division of the Selachians, which differ from their allies, and approach the following orders chiefly in the possession of an operculum (which is, how- ever, not supported by skeletal plates); the giU lameUas completely cover the side -of the septum, but do not project over its outer rim (Kg. 309 B). The skin is
Text Appearing After Image:
Fig. 314. ChimoBra monstrosa, ^. â for the most part naked, the mouth armed with a small number of large teeth. The upper portions of the mandibular and hyoid arches are attached to the skull. In other respects they exhibit for the most part the characters of other Selachians. One species, Ch. monstrosa, is abiindant in the Mediten-anean, on the coast of Noi-way, and elsewhere. Order 3. Ganoidei. The skeleton consists of cartilage and bone; conus arteriosus and spiral valve are present; an operculum supported by bony plates; -often a spiracle; swim-bladder or true lung. The skin usually

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