OCR Text |
Show 1899.] STRUCTURE OF LABORDE's SHARK. 733 of which the dimensions are given in the British Museum Catalogue of Fishes (vol. viii. p. 428), being a little less than 10 inches in leugth measured from the extremity of the snout to the tip of the upper lobe of the caudal. The skin, as in the British Museum individuals, is, regarded as a whole, of a uniform brownish-black colour, but while the proximal portion of the azygos and paired fins are of the same tint, the distal present a marked contrast, being of a dull yellowish hue. There is a well-marked mid-dorsal and an equally well-marked mid-ventral groove, and on either side, not far from the dorsal surface, a rather deep lateral groove runs backward nearly to the base of the caudal. The area occupied by the five branchial apertures is about 8 m m . in length, the last of the slits being immediately in front of the base of the pectoral. The individual gill-slits are very small (only 2 millimetres in length), while the spiracles, on the other band, are noteworthy for their large size; semicircular in outline, they measure 5 millimetres along the posterior border. O n the upper surface of the head are two well-marked curved longitudinal grooves, continuations forward of the lateral grooves already mentioned, connected by a transverse one situated immediately between the spiracles. Each of these grooves exhibits a series of pores (the openings of mucus-canals) which can be craced backward for some distance along the sides of the body. A row of pores further passes from the longitudinal groove of either side obliquely downward between the spiracle and the eye, and a second transverse row runs between the eye and the nostril to join a third row situated at right angles at some distance below the level of the eye. Additional pores more scattered in distribution occur in the skin covering the upper, and also in a less degree in that clothing the lower jaw. The nares occupy a considerable area near the tip of the snout, being removed from the mouth by a considerable interval. Their upper portion is rounded, and they are continued ventraily in the form of elongated slits overlapped by a valve of skin. The eyes are large, measuring 9 m m . in antero-posterior diameter. The scales are very small, communicaring a minutely granular appearance to the skin, which is almost smooth, there being hardly auy perceptible harshness to the feel when the fingers are passed along it from bead to tail or vice versa. Magnified a few diameters they appear in the form of slightly angular papilla). When isolated, after boiling a fragment in caustic potash, they exhibit irregularly lozenge-shaped outlines and possess an elevated central and a depressed marginal area with a slightly toothed edge. The aperture of the mouth at first sight appears much more extensive than it actually is, owing to a deep groove which runs backward from each angle. In the lower jaw only a single row of teeth are present. As noticed in Dr. Giinther's excellent diagnostic description, they are of considerable size, triangular in outline and non-serrated. The teeth of the upper jaw are much smaller, conical, and are disposed in three series. |