358 RAMSAY H. TRAQUAIR ON THE 
palato-quadrate apparatus, but probably teeth were present on the palate in 
this as in allied genera. The orbit is placed as in Hurynotus, but the circum- 
orbital plates are badly preserved, a large anterior one (lachrymal) may, how- 
ever, be clearly seen, as in that genus, over the fore part of the maxilla. 
The shoulder girdle presents us with well-marked post-temporal supra- 
clavicular, clavicular, and infra-clavicular elements, the three latter, at least, 
shaped exactly as in Hurynotus. The fin-rays are ganoid and sculptured ex- 
ternally, divided by transverse articulations up to their origins, their demi-rays 
imbricate in the anterior part of each fin, and fulcra are conspicuously present, 
though these are smaller than in Hurynotus. The pectorals are of moderate 
size, the ventrals well developed and abdominal. The dorsal reminds us strongly 
of that of Hurynotus, commencing opposite the ventrals, and having its anterior 
margin in the usual condition of expansion of the fin continuous with the line 
of the back between its origin and the occiput; its anterior rays become very 
rapidly elongated towards the high and acutely pointed apex, from which they 
again rapidly fall away posteriorly, so that the hinder two-thirds of the fin is 
low and fringe-like. The anal is similar in form, but smaller, and its posterior 
fringe-like part proportionally shorter, the entire length of the base of the fin 
hardly equalling two-thirds that of the dorsal. The caudal is strongly hetero- 
cercal, deeply cleft and inequilobate. 
The affinities of Mesolepis to Eurynotus are clearly seen in the form and 
position of the dorsal and ventral fins in the powerfully heterocercal and 
inequilobate caudal, as well as in the form and general osteology of the head. 
But the scales have now decidedly assumed the Platysomid type, the body is 
deeper in shape, and the anal fin too has begun to resemble the opposing 
dorsal, though its base is still considerably shorter. The teeth differ consider- 
ably from those of Hurynotus in external form, but in such cases where they 
have a constricted neck they in so far resemble those of Eurysomus, a genus 
long confounded with Platysomus, but which has really much more affinity with 
Mesolepis. In M. micropterus the form of tooth passes into that which is 
found in Platysomus. 
Genus IV. Eurysomus, Young, 1866. © 
Platysomus (pars), Agassiz, Egerton, et cet. auct. 
(2) Globulodus, Minster. 
The remarkable fish from the English marl slate, designated by Acassiz 
Platysomus macrurus, was first figured, though without any name, by Professor 
SEDGWICK.* At the time, however, of the publication of the “ Poissons Fossiles,” 
* Trans. Geol. Soc, Lond., ser. 2, vol, iii. plate xii, figs, 1 and 2. 
