420 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



the segmentation. They are thus in the condition of the anterior rays 

 of the dorsal fin of some of the large Catostomidce where they are prox- 

 imal ly homogeneous and bony, distally segmented and cartilaginous. 

 This is an important character when found in pectoral and caudal fins, 

 and such as I have not found described. It adds another feature to the 

 definition of this group. 



The segmentation above alluded to presents the following characters: 

 The spine consists of four principal parallel rods, of which the external 

 on each side thins, the one to an obtuse, the other to a thin edge. The 

 more obtuse edge presents a groove on one side, which is occupied by a 

 very slender rod, and a shallow rabbet along the flat edge is occupied by 

 a slender flat rod. Of the four principal rods the two median are the 

 most slender, and the flat marginal the widest. Of the two median, that 

 next the last is the wider. The stout marginal, or probably anterior 

 rod, is segmented en chevron, the angle directed forwards and lying 

 near the free margin. The suture of the segments is entirely straight, 

 except when returning it approaches the margin, where it suddenly 

 turns to the margin at right angles to it. The next rod is segmented 

 without chevron obliquely backward and inward ; where it leaves and 

 reaches the margins, it is at right angles to them, and the margin pro- 

 jects obtusely at those points. Between them the suture is very irreg- 

 ular and jagged, sending processes forward and backward. The seg- 

 mentation of the next rod is similar, but more regularly serrate; distally 

 it becomes as irregular as in the last. The transverse marginal termini 

 of the sutures are serrate in both. The inner and widest rod presents 

 a still more regularly serrate suture, with the truncate extremities; but, 

 owing to the width of the rod, the near approximation of the sutures 

 continues for a longer distance. When broken, the suture appears 

 step-like. 



This remarkably beautiful segmentation is paralleled remotely, as has 

 been stated, by some siluroids, but much more nearly by the external 

 caudal rays of elops. Much more like the recent type are the seg- 

 mented rays of the carboniferous genus, Edestus of Leidy, regarded 

 variously by authors as a jaw or a ray, but now generally regarded as a 

 ray. 



Measurements. 



Mi 



Length of fragment of (?) caudal spine 0.25 



Width of fragment at proximal fracture 06 



Greatest thickness at proximal fracture 013 



Width of posterior rod at proximal fracture 0245 



Length of six distal caudal vertebrae 10 



Width of haemal spine of second of series 024 



Vertical diameter of centrum, first series 025 



Length of neural spine and centrum of anterior caudal 108 



Transverse diameter of neural spine of anterior caudal at base . . .0235 

 Antero-posterior diameter of four anterior caudal neural spines 



in contact * 069 



Length of centrum of a dorsal 04 



Vertical diameter of a dorsal : . . .0615 



Transverse diameter of a dorsal, (crushed) 041 



These remains were found in place by Professor B. F. Mudge. He 

 states that their extent was eight feet. As they embrace no cervical 

 vertebras, nor portions of cranium, two feet are probably to be added, 



