348 RAMSAY H. TRAQUAIR ON THE 
STRUCTURE OF THE PLATYSOMIDZ. 
Before entering on the structure of the various genera, I must explain that 
the cranial roof bones of the Platysomide, being evidently, like those of the 
Paleoniscidee, entirely superficial or dermal in their nature, the terms 
“anterior” and “posterior frontal” are not used to designate bones abso- 
lutely identical with those so named in the Cuvierian nomenclature, for which I 
prefer Mr ParxkeEr’s terms, “ ectoethmoidal” and “ sphenotic.” The opercular 
bones being in this group also very similarly conformed to those in the Palzeo- 
niscidee, I shall, in accordance with the views expressed in my account of the 
last-named family, term that plate “interoperculum,” which has been hitherto 
known as ‘“ suboperculum.” 
Genus I. Eurynotus, Agassiz, 1835. 
Plectrolepis, Egerton, 1850 (Agassiz ?). 
Platysomus, Agassiz, pars (ML.S.) 
Platysomus, De Koninck, pars, 1878. 
Mistory.—Eurynotus is mentioned by AGAssiz in the report of the meeting 
of the British Association at Edinburgh in 1834, and also by H1ipBert- WARE in 
the “ Proceedings of the Royal Society of Edinburgh ” for December 1834, and 
in his Memoir on the Burdiehouse Limestone, in vol. xiii. of the Transactions of 
the same Society. Descriptions and figures of EL. crenatus from Burdiehouse, 
E. fimbriatus from Wardie, and E. tenwceps from Sunderland, Massachusetts, 
were given by AGassiz in 1835,* who considered the genus as “ Lepidoid,” and 
intermediate between Amblypterus and Platysomus—“ La forme de son corps et 
de sa nageoire dorsal le rapproche méme davantage des genres a corps plat, 
tandis que la forme des nageoires paires rapelle le genre Amblypterus.” Re- 
garding the teeth, he says that the margin of the inferior maxillary is armed 
with “ plusieurs rangées de dents extremement fines et obtuses,” but he seems 
to have mistaken the maxilla for a suborbital. Acassiz’s third species, £. 
tenuiceps, from the Triassic beds of North America, was subsequently ascer- 
tained by W. C. REDFIELD not to be a Lurynotus,t and it is now referred to Sir 
Putip GreY-EGErToN’s genus Jschypterus, belonging to a totally different 
family. . 
In 1850 Sir Puttip Grey-EceErton quoted a letter from Huca Miter rela- 
tive to the rounded palatal teeth of Hurynotus, having also received a cast of 
the specimen, but, as we have already seen, he did not consider these teeth as 
* Poissons Fossiles, vol. i. part i. pp. 153-160. 
+ Short Notices of American Fossil Fishes, “ Am, Journ, Se.” xli. 1841. 
