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Show 684 PROF. G. B. HOWES ON THE PECTORAL [Dec. 2, ferences between the shoulder-girdle of the Torpedinida? and the other Batoidei; and, among those characters which I have recounted, the mere articulation of the propterygium upon the mesopterygium is, in itself, insufficient to warrant the relegation of their fin-skeleton to the Trygonid category. The articulation named is absent in Hypnos; and, in view of the inconstancy of the pro- meso-pterygial articulation of Pteroplatea (ante, p. 677), it may justly be looked upon as of independent origin, probably in association with the demands of the electrical apparatus. The facts appear to me to strongly suggest the possibility of an independent origin for the Torpedinida?, as distinguished from other Batoids, and to warrant a suspicion that the suborder Batoidei as defined by Dr. Giinther ' may be at least dipbyletic. In this connection it is noteworthy that Smith Woodward has lately referred Pristis, through Sclerorhynchus, to a near kinship with the Pristiophoridce 2, and that examination of the pectoral fin-skeleton of that fish fully justifies his action2. Comparison of Rhina squatina with the Batoidei Ceratopterina, in which the pectoral fin is free of the head J, would seem to point in the same direction, and to indicate the independent association of these forms. The study of the fin-skeleton of Dicerobatis is, at this juncture, very desirable, but I regret to say that I have been unable to pursue it, for want of material. V.-The Pectoral Fin-Skeleton of the Rhinobatidse. The fin-skeleton of this family has been described by Gegenbaur for Rhinobatus, and more recently dealt with by Haswell for Trygono-rhina (I. c. pp. 39 et seq.). M y own observations have extended to Rhynchobatus also (cf. Table). Taking the three genera collectively, the mesopterygium (ms., fig. 8) may be regarded as a small plate, most nearly resembling that of the Raiidce but for its more regular and constant proportions (cf. figs. 4, 7, and 8). The rays which unite to form it are least numerous (from 4 to 5) in Rhynchobatus, most numerous in the two remaining genera; and the same holds good for the numerical variation observable in the intercalary rays. Examination of the Table which 1 append will show that the pectoral fin-skeleton of Raia radiata furnishes a very satisfactory connecting-link, between that of the other Raiidce and of the Rhinobatidce, and I conceive of that fish as much more lowly than the allied R. batis, R. clavata, and R. maculata. And, whatever is to be said for the surmised dipbyletic origin of the Batoidei taken as a suborder, the two families above named would appear to be more intimately related to each other than to any remaining family of the Batoids as ordinarily understood. The embryological data at our disposal warrant the belief that the forward rotation of the propterygium is a secondarily acquired 1 Catalogue of the Fishes in the British Museum, vol. viii. (1870) p. 434. 2 P. Z. S. 1889, p. 449. For a description and fig. of the Pristiophorus fin see Mivart, P. Z. S. pt. iv. 1879, p. 453, pi. lxxviii. 3 Cf. Giinther, Cat. cit. p. 496. |