30 THE CANADIAN NATURALIST. [Vol. X. 



As compared with the Plianeropleuron Andersoni of Huiley, 

 from the Old Pted Sandstone of Dura Den, the only previously 

 known species of the genus, the P. curtain appears to differ in its 

 smaller size, and more especially in its much greater height or 

 depth as compared with its length. Judging by the figures in 

 the tenth Decade of the " Memoirs of the Geological Survey of 

 the United Kingdom," the length of F. Andersoni is equal to 

 about five and a half times its height, whereas in adult or pre- 

 sumably adult specimens of P. curtinn, the length does not much 

 exceed twice the height. On a cursory examination the dorsal, 

 caudal and anal fins of the present species appear to be con- 

 tinuous, but a closer scrutiny shews that the bases of the caudal 

 and anal fins are separated by a short space. 



EnsTHENOPTERON,-'^ Gen. Nov. 



Generic Characters. Dermal plates of the head densely and 

 irregularly corrugated externally, the corrugations varying in 

 size in different parts of the same plate, but rarely or never 

 coalescing with each other so as to form a complete network. 

 The larger corrugations have a tendency to become tubercular. 

 Teeth, at least the smaller ones, compressed-conical, with a sharp 

 cutting edge on each side. Scales of the body, cycloid, imbri- 

 cating ; their exposed surfaces marked either with minute, close- 

 set, irregular, radiating, tubercular ridges, — or more rarely with 

 a semi-circular area of concentric rows of small, distant, isolated 

 tubercles, upon a surface ornamented with exceedingly fine, wavy, 

 radiating lines. Dorsal fins two, separated by an interval about 

 equal in length to the height of the body between them. Pec- 

 toral fins unknown. Ventrals small, short, broad and placed a 

 little behind the first dorsal. Anal fin large and broad, placed 

 opposite to the second dorsal. Caudal fin also large and broad, 

 heterocercal, with an unusually well developed upper lobe. 



Vertebral centres not ossified: neural and haemal spines and 

 inter-spinous bones well developed and completely ossified. 

 Neural and hagnial spines anterior to the second dorsal and anal 

 and for a short distance behind them, blade-like and flattened, 

 with more or less acute margins. Neural spines of the upper 

 lobe of the tail simple, much elongated, subcyliudrical and 



* From tv-odtvrjq^ stout, and Trrepov, a fin, in reference to the strongly 

 developed anal and second dorsal. 



