318 Dr. A. Giinther on the Young State of Fishes centrum so short as the early caudals oi Acanthopholis^ and all differ in the neural arch, the transverse process, the ab-sence of horizontal lateral ridges, and greater compression of the body of the centrum from side to side. In birds the tail is not similar. But among mammals of many kinds there is a closer ap-proximation to the Dinosaurian tail in proportion, form, and detail of vertebra than is seen in the crocodile, even the neural arch becoming singularly small in the Dinosaur. These mammalian resemblances, supposing them to be essential Dinosaurian structures, would tend to indicate a common parentage for Dinosaurs and Mammals in the ornithodelphian direction, and not that there were similar vital organs for the Mammalian and Dinosaurian tjrpes. And probably the time is near when the student of osteological synthesis, endeavouring to emulate the achievements of the astronomer predicting the orbits of new planets, will be able to characterize orders and perhaps whole classes of extinct and undiscovered animals from the evidence of their structures inherited in the types which survive. EXPLANATION OF PLATE VII. Fi(f. 1. Front view of the metapodium oi Acanthoiiholis platypus. Fig. 2. The proximal ends of the same metapodial hones. These figures are half natural size, and from photographs hy A. NichoUs, Camhridffe. XXXVIII. — On the Young State of Fishes helonging to the Family of Squamipinnes. By Dr. Albert Gunther, F.R.S. In the first volume of the present series of this Journal (1868, p. 457) I described and figured a very small fish, 11 millims. long, under the name of Tholichthys. Its head was armed in a most peculiar manner (by large suprascapular, humeral, and prseopercular laminee) ; and, although I had but little doubt that the appearance of old or mature examples would be dif-ferent, I did not think it possible that the osseous plates be-hind the head would disappear entirely. I considered it to be the type of a Cyttoid genus. Since that time I have examined several other Tholichthyes. Lieut.-Col. Playfair obtained some from Zanzibar (where also the original example was discovered) ; but they were of the same small size, and did not differ from the first example, except that the dorsal spines appeared to be more numerous and apparently somewhat variable in number. Surgeon Day found other similar fishes at Madras ; but they
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