Reviews — Palceozoic Fishes. 233 



Cause of an Ice Age " is not the pi'oduction of a professed brother 

 of the hammer, nevertherless it will well repay perusal, and all 

 must acknowledge that a valuable contribution has been made by a 

 distinguished ally, bearing upon one of the most difficult problems 

 of our science. 0. Fishek. 



II, — Paleozoic Fishes. 



1. On the Characteks of some Paleozoic Fishes. By E. D. 

 Cope. Proc. United States National Museum, VoL XIV. (1891), 

 pp. 447-463, Pis. XXVIII.-XXXIII. 



2. Ueber Ptericbthts. By J. Victor Eohon. Verhandl. Euss. 



Kais. Mineral. Ges. St. Petersburg, Vol. XXVIII. (1891), pp. 

 [1-25 reprint], PI. VII. 



OUR knowledge of the Palaeozoic Fishes is still progressing 

 rapidly both in Europe and America, and we have lately 

 received the two papers on this subject quoted above. Prof. Cope's 

 communication is divided into seven parts, and deals with several 

 important types ; Dr. Rohon's work is chiefly an examination of the 

 histological structure of the shield of Pterichthys. 



The first fossils noticed by Prof. Cope are referable to Elasmo- 

 branchii. A detatched tooth from the supposed Permian of eastern 

 Nebraska, named Stijpiohasis Knightiana, is very remarkable on 

 account of the small size of its base of insertion ; we should, indeed, 

 prefer to have some information as to its microscopical structure 

 before accepting the fossil definitely as an Elasmobranch tooth. 

 A typical spine of Gtenacanthus {C. ambJyxiphias, sp. nov.) from the 

 Permian of Texas is a noteworthy discovery ; and the first truly 

 hybodont fin-spine met with in the New World {Hybodus regularis, 

 sp. nov.) is also of much interest, though it is not Palaeozoic, being 

 from the supposed Trias of Baylor Connty, Texas. 



The Elasmobranch fi-agments are only of limited importance, but 

 Prof. Cope's description of the cranium of MacropetalicJiihys — one 

 of the most remarkable and least understood American Arthrodira or 

 " Placoderms " — tends towards a considerable advance in our know- 

 ledge of the great extinct gi'oup of fishes to which it belongs. As 

 pointed out by Prof. Cope, this genus is not related in any way to 

 the Sturgeons, notwithstanding the contrary assertions of several 

 observers; and the plates of the head-shield are shown to be 

 arranged much as in Coccosfens, Dinichthys, and the other Arthrodira. 

 The hinder part of this shield, it is stated, " does not seem to have 

 protected the brain, but rather the anterior part of the vertebral 

 axis, and seems to have been a nuchal plate." Exactly the same 

 opinion has already been expressed in reference to the so-called 

 "occipital region" of the Scottish Homosteus (Proc. Zool. Soc. 1891, 

 pp. 198-201). The base of the cranium in an Arthrodiran is now 

 described for the first time. Professor Cope's specimens of Macro- 

 petalichfJiys displaying a good deal of this region ; and the detailed 

 anatomical description is followed by a discussion of the relationships 

 of this type of fish in the light of the new facts adduced. On the 



