684 PROF. G. B. HOWES ON THE PECTORAL, [DcC. 2, 



ferences between the shoulder-girdle of the Torpedinidcs 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 Torpedinidm, as 

 distinguished from other Batoids, and to warrant a suspicion that 

 the suborder Batoidei as defined by Dr. Giinther ' may be at 

 least diphyletic. In this connection it is noteworthy that Smith 

 "Woodward has lately referred Pristis, through SclerorhyncJius, to a 

 near kinship with the PristiophoridcB ', and that examination of the 

 pectoral fin-skeleton of that fish fully justifies his action '\ Com- 

 parison oi Rhina squatina witii the Batoidei Ceratopterina, in which 

 the ])ectoral fin is free of the head ', would seem to point in the same 

 direction, and to indicate the independent association of these forms. 

 The study of the fin-skeleton of Dicer obatis 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 Rhinobatidae. 



The fin-skeleton of this family has been described by Gegenbaur 

 for Rhinobatus, and more recently dealt with by Haswell for Tryyono- 

 rhina (/. c. pp. '69 et seq.). My own observations have extended to 

 Rhyrichobatus 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 Rhinohatidce, 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 diphyletic 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 



^ Catalogue of the Fishes in the British Museum, vol. viii. (1870) p. 434. 

 * P. Z. S. 1889, p. 449. For a description and fig. of the Pristio^horus iiu see 

 Mivart, P. Z. S. pt. iv. 1879, p. 453, pi. Ixxviii. 

 » Cf. Giinthei-, Cat. cit. p. 496. 



