1849.] 



EGERTON ON THE GENUS PLATYSOMUS. 



329 



January 31, 1849. 

 The following communications were read : — 



1. Description of Remains of Fossil Reptiles from the Greensand 

 Formation ofi^^MV Jersey. By Prof. Owen, F.R.S., F.G.S. &c. 



[See an Abstract of this Paper, p. 380.] 



2. Palichthyologic Notes. No. 2. — On the Affinities of the Genus 

 Platysomus. By Sir Philip Grey Egerton, Bart., M.P., 

 F.R.S. 



Some of the earliest writers on Palaeontology were acquainted with 

 the Petrified Fishes not uncommonly found in the Kupferschiefer of 

 Mansfeld and its vicinity, on which Agassiz established his genus 

 Platysomus. Figures are given of these fishes under the name of 

 Rhombus diluvianus major and minor, by Wolfart *, Scheuchzer f , 

 Knorr and Walch X^ and others. More recently De Blainville and 

 Germar have described them, assigning them, in consequence of their 

 deep and flattened forms, to the genus Stromateus^. Agassiz satis- 

 fied himself that this determination, founded on outward characters, 

 unaccompanied by structural coincidences, could not stand || ; at the 

 same time the unusual combination of this form of body with a hete- 

 rocerqual tail and other anatomical peculiarities evidently raised 

 doubts in his mind as to the true position and affinities of the genus ^. 

 Mr. King of Newcastle-on-Tyne has recently submitted to me a speci- 

 men of Platysomus macrurus from the magnesian limestone of Ferry 

 Hill, which clears up the obscurity that has hitherto enveloped the 

 subject, and proves from 



the characters of the denti- ^S' 



tion that this genus should 

 be removed from the Lepi- 

 doidei to the Pycnodonti. 

 The dentary portion of the 

 lower jaw, as shown by this 

 specimen, fig. 1, is a dense 

 triangular bone, very similar 

 to thePycnodont jaws found 

 atStonesfield and elsewhere. 

 Two rows of teeth are seen, 

 the outer one composed of 

 eight or nine small tritores, 

 the inner one containing five 

 considerably larger than the 



outer ones. The teeth are all clavate in form. The crown is cir- 

 cular, slightly flattened on the grinding surface, and mounted on a 

 pedestal of smaller diameter. Immediately beneath the crown is a 

 deep constriction, beyond which the enamelloid coating of the tooth 



* Wolfart (Peter), Historia naturalis Hassiae inferioris, pars i. tabs. 13, 14. 



t Scheuchzer, Piscium Querelre, tab. 4. 



X Knorr and Walch, vol. i. pi. 20. 



§ Nouv. Diet. d'Histoire Nat. vol. xxviii. p. 18. 



11 Poiss. Foss. vol. ii, part 1. p. 161. \ Ibid. p. 162. 



