PINS OF GANOIDS AND TELEOSTS. 591 



the elements remain bisegmental, more or fewer o£ the anterior 

 ones become specialized for the support of powerful defensive 

 spines, and in consequence lose their distal segments and become 

 unisegmental, as, for example, the first two elements of the dorsal 

 fin. On the other hand, in the Gymnotidse the distal segments 

 are either entirely wanting or are represented by simple fibrous 

 pads interposed between the fin-rays and the distal extremities 

 of the proximal segments. 



It is nevertheless interesting to note that in the Clupeidae and 

 Siluridse, as in so many other Teleosts, the distal extremities of 

 the proximal radial segments of the dorsal fin, with the occasional 

 exception of the more anterior of the series, are produced 

 obliquely upwards and backwards into well-marked postero- 

 superior processes, which in their relations to the distal segments, 

 as well as in their articulation with the proximal segments of the 

 next succeeding elements, exhibit a striking resemblance to the 

 mesial segments of Amia and Lepidosteus and of those Physostomi 

 with trisegmental elements. There is, however, no evidence that 

 these processes are mesial segments whicb have fused witb the 

 proximal segments, or that they can be looked upon in any other 

 light than as modifications of the distal extremities of ordinary 

 proximal segments that have taken the place of the missing 

 mesial segments ; and this conclusion is supported by tbe fact that 

 in some Teleosts (e. g. Regalecus) similar processes, but antero- 

 superior in position, may be developed from the distal ends of 

 the proximal segments and exist in conjunction witb ordinary 

 postero-superior processes *. In the Characinidae {Cltharinus) 

 these processes are entirely wanting, and the proximal segments 

 derive mutual support from the simple apposition of their distal 

 extremities. In the G-ymnotidae {G-ymnotus) not only are 

 postero-superior processes undeveloped, but the proximal seg- 

 ments have no articular relations, and except for their ligamentous 

 connexion are quite distinct from one another t. 



As regards the ossification of the radial elements, the proximal, 

 and the mesial segments when present are invariably ossified : 



* It is not altogether improbable, however, that a proximal segment and its 

 poster o-saperior process may correspond to Harrison's " Flossenstrahltrager," 

 and therefore represent an undivided proximo-mesial segment ossified continu- 

 ously from a single centre. 



t The -proximal radial segments of the anal fin very generally possess 

 oblique postero-inferior^processes which are smilar in their mutual relations to 

 the postero-superior processes of the dorsal fin. 



