Dr R. H. Traquair on Chondrosteus acipenseroides. 349 



XXVII. Notes on Chondrosteus acipenseroides, Ar/assk. By 

 Dr E. H. Traquair, F.RS., F.G.S. 



(Read 20th April 1887.) 



The now well-known Liassic Acipenseroid fish Chondrosteus 

 acipenseroides was named by Agassiz in 1843, but not de- 

 scribed by him.i It subsequently formed the subject of an 

 elaborate memoir by Sir Philip Grey-Egerton, Bart. ,2 in 

 which, besides giving a minute account of the structure of 

 the genus, he named two additional species — C. pachyurus 

 and C. crassior. Putting the results of Sir Philip's investi- 

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

 all essential points " Chondrosteus resembled the recent Stur- 

 geon, 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. More- 

 over, the skin of the body presented 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 six lines ^ is given in the Quarterly 

 Journal. The object of the paper was to show that Chon- 

 drosteus 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 1887 I placed the family " Chondrosteidse " (including 

 Chondrosteus) in the "Acipenseroid" suborder of Ganoids, 

 between the Spatularidse and the Palseoniscidse, which latter 

 family, along with the allied Platysomidse, 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 Geolo- 



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

 - Phil. Trans., voh 148 (1858), pp. 871-885. 

 '^ Quart. Journ. Geol. Soc, vol. xxii. (1866), p. 596. 



^Ganoid Fishes ofthe British Carboniferous Formations, Pt. I. Palseoniscidae, 

 p. 42, Pal. Soc, 1877. 



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