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Show 536 MR. A. S. WOODWARD ON [Dec. 7, ment. The latter (mtp) is triangular in form, and elongated antero-posteriorly; the foremost border abuts against the hinder edge of the preaxial cartilage, which it equals in transverse extent ; and the inner border curves gradually outwards and backwards to meet the nearly straight external boundary at a posterior apex. Judging from the analogy of living Selachians with fins of a similar type, the posterior of these cartilages may be regarded as the metapterygium ; while the anterior element may represent the coalesced pro- and mesopterygium (as in Pristiophorus1), or it may be wholly meso-pterygial, with a minute, indistinguishable propterygium at its proximal angle (as in Heptanchus and Hexanchus ). Beyond the basal cartilages are arranged the cartilaginous rays of of the fin (r). These are somewhat obscured both in front and behind by remains of the integument, and it is uncertain whether the first attached to the preaxial element is stouter than the remainder; twenty rays, however, can still be counted on the right side, and there are traces of sixteen on the left; the foremost thirteen are directed almost transversely or outwards, while the following have a more marked backward inclination. The pelvic girdle and its appendages are rather more satisfactorily displayed than the pectoral structures just described. Anteriorly, on each side, the cartilage is prolonged into a remarkably strong prepubic process (p.pb), the base of which occupies one fourth of the entire breadth of the girdle ; but the forward extent of the prominence is not determinable, owing to imperfect preservation. Posteriorly, on each side, is a long slender iliac process (il), especially well seen on the left, and slightly directed outwards; it is much less robust than the prepubic, and appears of almost uniform breadth throughout; in length it equals twice the width of the transverse pubic cartilage (pub). Arising immediately within the point of union of the pubic and iliac regions is the basal cartilage (b.s) of the pelvic fin, which exhibits no sutural divisions, and (this specimen being a male) is prolonged backwards into a powerful clasper (cl). It curves gradually inwards throughout the whole of its rayed portion, and is of almost uniform breadth. On passing into the claspers, the cartilage becomes more calcified, and perhaps slightly broader. The inner edge is straight, but the outer edge exhibits a gentle sigmoid curve, which results in the widening of the rounded terminal extremity; and at the end of each clasper (especially the left) a small tuft of dermal booklets (hk) is preserved. The fin-rays (r), which appear to be completely shown on the right, are altogether twelve in number, and the length of the supporting cartilage is scarcely more than one half of that of the appended clasper. There is no distinct evidence of one or more preaxial rays attached to the girdle itself, and the foremost exhibited is no longer than the remainder. 1 St. G. Mivart, " Fins of Elasmobranchs," Trans. Zool Soc. vol. x. p. 453, pi. lxxviii. fig.l. 2 C. Gegenbaur, " Schultergiirtel der Wirbelthiere, und Pru.stflosse der Fiscbe," Untersuch. vergl. Anat. Wirb. 1865, pi. ix. figs. 1, 2. |