| OCR Text |
Show 1886.] SQUALORAJA POLYSPONDYLA. 535 Vertebral Column.-In the subject of fig. 1 the vertebral column is beautifully shown beyond the shoulder-girdle, though somewhat imperfect in front. As already described by previous writers, the vertebrae (fig. 8) are merely slender, concentrically marked rings, of the truly " tectospondylic " 1 type, and in the space just mentioned no less than 340 can be counted; in the abdominal region, sixteen of these occupy the length of a centimetre, while in the tail the proportions are so slightly different that only one more ring is comprised within the same distance. The obscure portion in front of the pectoral girdle measures one and a half centimetres in length, probably representing about 24 vertebrae ; and if three centimetres are missing from the end of the tail2, this loss will indicate an additional 48. The total number is thus found to be approximately 400, as estimated by Davies in the large specimen described in 1872. In the more aged individuals (e. g., no. II.) the vertebral rings are more robust than those of the apparently young (e.g., no. III.) ; and it is remarkable that in no example is there any trace of the fusion of the elements in the region of the neck. But it is not necessary to add a detailed account of the structure of the vertebrae themselves, for they have already been carefully examined and described by no less an authority than Professor Carl Hasse, of Breslau3. As the result of his researches in this direction, the latter anatomist concludes that in Squaloraja "we have to do with an ancestral form of the now living Pristidae, a form which, in its development, appears to have advanced beyond the existing Pris-tiophoridae, and also beyond the oldest Rhinobatidse," which he has described from the upper Oolite of Bavaria. The vertebral arches were not of sufficient consistency to leave the slightest trace in toe fossil state. Appendicular Skeleton.-In the subject of fig. 1, as already remarked, the pectoral fins are sufficiently well preserved to exhibit their complete severance from the cephalic region and their correspondence in general character to those of the living Pristiophorus. But the remains of the supporting girdle are much less perfect and satisfactory, and the other known specimens do not appear to throw any further light upon the subject. There can be little doubt, however, that the " girdle " was complete, as in the Rays proper, and the well-defined cartilage (s.sc) on the right is evidently the characteristic suprascapula. A faint trace of the posterior boundary of the transverse coracoid bar (cor) is also shown on the same side. The proximal cartilages of the fin are only two in number, and well preserved on both sides of the fossil, though most completely displayed on the left. The preaxial element (pms) is elongated in a transverse direction, and appears of almost uniform breadth, though its exact shape is evidently destroyed by crushing ; it is relatively small, having only about one quarter the size of the postaxial ele- 1 C. Hasse, 'Das natiirliche System der Elasmobrancbier,' allgemeiner Theil (1879), p. 44. 2 The caudal region of the fossil is not completely shown in fig. 1. 3 C. Hasse, " Einige seltene palaoutologische Funde," Palteontographica, vol. xxxi. (1885) p. 4, pi. i. figs. 2, 3. |
