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Show 1886.] SQUALORAJA P O L Y S P O N D Y L A . 53/ AFFINITIES AND SYSTEMATIC POSITION. Proceeding, lastly, to a consideration of the systematic position of Squaloraja, it will be observed that the new fossils here described enable us to arrive at a much more definite conclusion than it has hitherto been possible to formulate. Agassiz has pointed out the affinities of the genus with the Pristiophoridae ; Davies has further indicated some resemblances to the Rhinobatidae, and been led, by his discovery of the rostral spine, to speculate at least as to its family distinctness ; while Giinther1 has likewise refrained from more than a suggestion that it is nearly allied to the first-named group. That the animal is a true Selachian, there cannot be the slightest doubt; nor does it require more than a superficial glance to recognize its resemblance both to the Sharks proper and the Rays. But (as already mentioned by Davies) the possession of a prehensile rostral spine by the male distinguishes Squaloraja from all known members of the order, recent or fossil, and suggests affinities with the Chi-maeroids 2; while the enormous size of the barbels or cirri seems to have no parallel, at least among living forms. The dentition, too, is evidently unique, so far as our present knowledge extends, and the marked character of the symphysis is a feature of peculiar interest. Comparing the genus in other points with the various recognized families upon the "borderland" of the two sections of the Selachii, reference may first be made to the Rhinidae. Though agreeing with this group in the very slight depression of the body, it is readily distinguished by the elongation of the snout and the inferior position of the mouth ; and the anterior border of the pectoral fin is much less produced forwards, owing to the relatively smaller size of the propterygium. To the oft-mentioned Pristiophoridae, Squaloraja bears a remarkable resemblance, both in the structure of the snout and the general form of the body ; but there are no traces of teeth on either boundary of the rostrum ; and if the peculiar dental armature of the jaw may be quoted as a family character, this, too, will exclude the genus from the present group. From the family of Pristidae, the Liassic form is still further separated by the characters of the head and its anterior prolongation, though agreeing tolerably well in the shape of the trunk and fins. There are also certain features that prevent its reference to the Rhinobatidae. The structure of the pectoral fin in this family is quite distinct from that of the fossil, the propterygial element being prolonged far towards the head, so that in some cases it is connected by skin with the cephalic region. Its distinctness from other families is too obvious to require any special mention, and Squaloraja is thus excluded from all recognized divisions of the order. It may even represent a hitherto unknown 1 A. Giinther, ' Study of Fishes ' (1880), p. 335. 2 W e regard the Chimai'roiilei as a distinct order, follow ing Professor Huxley, Proc. Zool°Soc. 1876, p. 57. |
