535 



1870.] [Cope. 



are in their distal portions remarkably and beautifully segmented, of 

 wbicb a very simple form has been figured by Kner, as existing in the 

 pectoral spine of the Siluroid genus, Pangasius. This segmentation 

 becomes more obscure proximally, and finally disappears altogether, 

 leaving the spine and rods homogeneous. This portion of them is quite 

 identical -with the rods fovuid in the positions of fins, already described, 

 and I therefore regard these as fin radii of the attenuated form presented 

 by cartilaginous rays of most fishes, but ossified sufficiently to destroy 

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

 of the dorsal fin of some of the large Catostomidse, where they are 

 proximally homogeneous and bony, distally segmented and cartilaginous. 

 This is an important character vrhen 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 thp 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 dii'ected 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 backwards and inwards ; where it leaves and reaches the 

 margins, it is at right angles to them, and the margin projects obtusely 

 at those points. Between them the suture is very irregular and jagged, 

 sendincf processes forwai'ds and backwards. The segmentation 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. Much more like the recent type are the 

 segmented 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. M. 



Length fragment of (?)caudal spine 0.25 



"Width " at proximal fracture 06 



Greatest thickness " " ,013 



Width posterior rod " " 0245 



Length of six distal caudal vertebrae , .10 



