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 



