248 Dr. JR. IT. Traquair — On Chondrosteus acipenseroides. 



II. — Notes on Cbonbuosteus acipenseroides, Agassiz. 

 By Dr. R. H. Traquair, F.R.S., F.G.S. 



THE now well-known Liassic Acipenseroid fish Chondrosteus 

 acipenseroides was named by Agassiz in 1843, but not described 

 by liim.'^ It subsequently formed the subject of an elaborate memoir 

 by Sir Philip Grey-Egerton, Bart.,^ in which, besides giving a minute 

 account of the structure of the genus, he named two additional species 

 — C. pacJiyurus and C. crassior. Putting the results of Sir Philip's 

 investigations as briefly as possible, he maintained that while " in 

 all essential points " Chondrosteus resembled the recent Sturgeon, 

 nevertheless in certain others, and notably in the structure of the 

 opercular and hyoid regions, it constituted a transitional form towards 

 the more ordinary Ganoids. Moreover, the skin of the body pre- 

 sented the same naked condition seen in the recent Polyodon. 



Eight years afterwards Professor Young read a paper on the 

 subject before the Geological Society of London, of which only an 

 abstract of sis lines ^ is given in the Quarterly Journal. The object 

 of the paper was to show that Chondrosteus was a Holostean, not 

 a Chondrostean, because it "possesses a well-ossified basioccipital, 

 and the lateral walls of the cranium are composed of bones answering 

 to the cartilage bones of ordinary Teleostei." 



In 1877 I placed the family " Chondrosteidee " (including Chon- 

 drosteus) in the " Acipenseroid " suborder of Ganoids, between the 

 Spatularidge and the Palseoniscidge, which latter family, along with 

 the allied Platysomidee, I proposed to include in one great group 

 with the Sturgeons.* 



On the 9th March of the present year, Mr. J. W. Davis read a 

 paper on Chondrosteus acipenseroides before the Geological Society 

 of London, of which an abstract has been published. In this paper 

 Mr. Davis interpreted the appearances presented by a single fine 

 specimen in his own collection, and besides giving a detailed account 

 of its anatomical structure, expressed his belief " that there is no 

 specific difference between C. acipenseroides, Agassiz, and C. crassior, 

 Egerton." 



Mr. Davis does not seem, however, to have made use of the 

 magnificent suite of specimens of Chondrosteus in the British 

 Museum, which contains not only the types of Sir Philip Egerton's 

 figures, but also a splendid array of additional examples, mostly 

 also from the Egerton and Enniskillen Collections. For the privi- 

 lege of examining these, and of noting several new and interesting 

 details presented by them, I am indebted to Dr. Woodward, F.E.S., 

 Keeper of the Geological Depai'tment, and my thanks are due also 

 to Dr. Geikie, F.E.S., and Mr. E. T. Newton, F.G.S., for kindly per- 

 mitting me to take notes of the specimens in the Museum of Practical 

 Geologj'^, Jermyn Street. In the present paper I propose to give an 



^ Poissons Fossiles, t. ii. pt. 2, p. 280. 



2 Phil. Trans, vol. 148 (1858), pp. 871—885. 



3 Q. J. G. S. vol. xxii. (1866), p. 596. 



* Ganoid Fishes of the British Carboniferous Formations, Pt. I. Palffioniscidse, 

 p. 42, Pal. Soc. 1877. 



