200 



expanded laterallj' and straight. The latter gives olFa transverse prominence, 

 like half a globular knob, before reaching the extremity. Just within the 

 latter are two lai-ge foramina, which are connected with the extremity by a 

 groove on eacl^^side, which meet in a notch where the thin edge passes into 

 the knol). 



Both sides of the neural and hasmal spines are concealed in this species 

 and in the Ichthyodectes jyrognathus by numerous parallel osseous rods, which 

 are somewhat angulate in section. They lie along the centra of the anterior 

 series of caudal vertebrae, but are not to be found on vertebrse of any other 

 part of the column. Numerous loose and fragmentary rods of the same char- 

 acter accompany the loose and attached caudal vertebrae, and all of them 

 according to Professor Mudge, belong to the "posterior swimming organ" of 

 this animal. There is also a collection of these rods from the anterior region 

 of the body, which Professor Mudge thought occupied the position of an 

 anterior limb. They do not, any of them, present a segmentation such as 

 would be exhibited by the cartilaginous radii of caudal and pectoral fins, and 

 their nature might have remained doubtful but for the explanation furnished 

 l)y the anterior compound ray or spine of the posterior, probably caudal, fin. 

 Tliis ray, as in the case of the pectoral spine and first anal rays of some exist- 

 ing siluroid and loricariid fishes, is composed of a number of parallel rods 

 closely united. These are in their distal portions remarkably and beauti- 

 fully segmented, of which a very simple form has been figured by Kner, as 

 existing in the pectoral spine of the siluroid genus Pangasius. This seg- 

 mentation becomes more obscure proxiraally, and finally disappears alto- 

 gether,- leaving the spine and rods homogeneous. This portion of them is 

 quite identical with the rods found in tlie positions of fins already described, 

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

 l)y 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 CatostomidcR, or marginal caudal rays of some 

 Ghnracinidce, where they are proximally homogeneous and bony, distally seg- 

 mented and cartilaginous. 



The segmentation above alluded to presents the following cliai'aclers 

 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 slen- 



