STRUCTURE AND AFFINITIES OF THE PLATYSOMIDA. 359 
Agassiz had not himself seen a specimen, and he therefore contented himself 
with the reproduction of SEDGwicx’s figures and a few general remarks as to 
the leading peculiarities of external form which distinguished it from the 
associated Platysom.* But a much finer specimen, now in the Newcastle 
Museum, afterwards turned up, in which not only the entire shape of the fish 
but also the dentition of the lower jaw was preserved, and having been submitted 
to Sir Paitie Grey-EcGeErron, the mandible was figured by him in the “ Quarterly 
Journal” of the Geological Society,t the entire specimen in Kine’s “ Permian 
Fossils.”{ The peculiar form of the teeth as here shown, in which “ a. circular 
crown with flattened grinding surface” was “mounted on a pedicle of much 
less diameter,” was attributed by Sir Puiiip to the whole of the species then 
included under Platysomus, and, as we have seen in the introduction, was, 
along with some other circumstances, especially the form of the scales, con- 
sidered by him to warrant the removal of Platysomus, of which Gilobulodus, 
Minster, was now considered a synonym, to the family Pycnodontide. We 
have, however, also seen that although Agassiz concurred in this view, Pro- 
fessor Youne refused to accept the dentition of Platysomus macrurus as 
characteristic also of the true Platysomi, such as P. gibbosus, &c., and proposed 
therefore to institute for the former the new genus Ewrysomus. With Professor 
Youne, I must certainly agree as regards the distinctness of the genus from 
Platysomus, but at the same time it must be remembered that the resem- 
blance of the teeth of Hurysomus macrurus to those of Gilobulodus elegans is 
so great that were we only quite certain as to the generic identity in this 
latter case, MUnstrEr’s name would certainly be entitled to preference over, 
Dr Youne’s. 
Species.—Only one species of Hurysomus, viz., EH. macrurus, Ag. sp., has 
with certainty been determined. With this, Platysomus Fuldai of MUNSTER, is 
no doubt generically identical, and the latter has also been merged specifically 
in “ macrurus” by GEINITZ. 
Geological Distribution.—Eurysomus has as yet only occurred in strata of 
Permian age; in England in the marl slate; in Germany in the Kupfer- 
schiefer. 
Structure.—I am not in a position to enter minutely into detail regarding 
the structure of Hurysomus, the only specimens which I have seen being that in 
the Newcastle Museum, and a not very perfect head in the Edinburgh Museum 
of Science and Art. But no one can look at any of the published figures of 
the fish without being struck by the evident affinity which it bears to Mesolems, 
both in its general aspect and in the form and position of its fins. We have a 
* Poissons Fossiles, vol. ii. plate i. p. 170 ; Atlas, vol. ii. plate xviii. figs. 1 and 2. 
+ Vol. v. (1849). 
{ Mem, Paleontographical Society (1849), plate xxvi. fig. 1. 
VOL. XXIX. PART I, 4Z 
