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X.—On the Structure and Affinities of the Platysomide. By Ramsay H. 
Traquair, M.D., F.R.S.E., Keeper of the Natural History Collections 
in the Museum of Science and Art, Edinburgh. (Plates III.-VI.) 
(Read 5th May 1879.) 
INTRODUCTION. 
The genera, which I at present include under the family term Platysomide , 
are the following :— 
. Eurynotus, Agassiz. 
. Benedenius, Traquair. 
. Mesolepis, Young. 
. Lurysomus, Young. 
. Wardichthys, Traquair. 
. Chetrodus, M‘Coy. 
7. Platysomus, Agassiz. 
aor FO DS = 
Eurynotus and Platysomus (incl. Hurysomus) were classified by AGaAssiz in his 
Lepidoid family of Ganoids, the former genus forming in his opinion a transition 
between the latter and Amblypterus.* By GiEBEL, Hurynotus and Platysomus 
were included in his “ Heterocerci Monopterygii,” along with the Palzonis- 
coid genera known at that time, and unfortunately also along with ceriain 
other very heterogeneous elements (Hugnathus, Conodus, Megalichthys).+ By 
QvuensteDT Platysomus was also placed among the Heterocercal Ganoids, 
immediately after Palwoniscus, Amblypterus, and Pygopterus.t 
But already, before the appearance of QUENSTEDT’S ‘‘ Handbuch,” Sir PHILIP 
Grey-Ecerton § advocated the removal of the genus Platysomus to the family 
Pycnodontide on the following grounds:—The mandible of a specimen of 
Platysomus macrurus, Agassiz, from Ferry Hill, showed two rows of peculiar 
teeth with flattened crowns, supported on constricted necks, the dentary 
element of the jaw on which they were placed being also a “ dense triangular 
bone, very similar to the Pycnodont jaws found at Stonesfield and elsewhere.” 
* Poissons Fossiles, vol. ii. pt. 1, p. 153. + Fauna der Vorwelt, vol. i. pt, 3, Leipzig, 1848. 
{ Handbuch der Petrefactenkunde, Tiibingen, 1852. 
§ On the Affinities of the Genus Platysomus, “Qu. Journ. Geol. Soc., London,” v. (1849), p. 329-332. 
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