THE DEVONIAN EOCKS OF CANADA. 79 



the osselets are very stout and greatly elongated, but they rapidly decrease both in length 

 and size as they approach the posterior termination of the vertebral column. The haemal 

 spines of the tail, like the osselets, are contracted at or about the middle and expanded 

 at each end, but the hœmal spines are invariably much shorter than the osselets. All the 

 fin rays, including those of the tail, are composed of a great number of rectangularly 

 divided, short articulations. Fin rays of the second dorsal and anal fin each proceeding 

 from three osselets of unequal size, which are articulated to short prominences, separated 

 by corresponding concave emarginations, in the posterior half of the greatly expanded 

 outer extremity of a broad interspinous apophysis, in the manner shewn in the accom- 

 panying woodcut. 



Fig. 1.— Outline of interspinous apopliysis and osselets of the second 

 dorsal fin of Eustlienopteron Foordi. Natural size. 



" EUSTHENOPTERON POORDI, Sp. NoV. 



" Specific Characters. — Fish large, attaining a length of two feet or more ; first dorsal 

 fin very long, narrow and tapering to an acute point behind.' 



" In the sculpture of its cranial plates, in the shape and ornamentation of its scales, 

 and in the fact that the fin rays of its second dorsal and anal fins are both supported by 

 three osselets articulated to a broad interspinous apophysis, this genus somewhat closely 

 resembles the Tristiclwpterus of Sir Philip Egerton. But the vertebral centres of Tristi- 

 chopterus are said to be ossified, and the osselets of the lower lobe of the tail are described 

 as ' springing from eight or nine interspinous bones,' whereas in Eusthenopteron the 

 vertebral centres are not ossified and the caudal osselets are articulated to the hœmal 

 spines. Moreover, the bony svipports of the anal and second dorsal fins are much larger 

 and more fully developed in Eusthenopteron than they are in Tristichopterus. Thus, in 

 Eusthenopteron the length of the osselets of the anal fin is equal to four-fifths of that of 

 the apophysis to which they are attached, and the breadth of the mvich dilated outer end 

 of the same apophysis is equal to rather more than one-half of its length. In Tristichop- 

 terus, on the other hand, the osselets of the corresponding fin are less than half the length 

 of the apophysis from which they spring, and the slightly expanded oiiter extremity of 

 the apophysis is not much more than a third of its entire length. 



" The generic and specific characters oïE. Foordi ha,ye been drawn up from a number 

 of more or less imperfect specimens. The posterior half of the exoskeleton of the species 

 is well seen in a specimen about one foot long, in which, however, the caudal, anal and 



' The first dorsal has since been found to be smaller and neither any longer nor much more acutely pointed 

 than the second dorsal. 



