riK"S OP GANOIDS AND TELEOSTS. 599 



In the Spliyrgenidse and the Cottidae may be found examples of 

 peculiar methods of articulation which are different from any of 

 those hitherto considered. In the former of the two families the 

 distal radial segments have no hook-like processes, and the base 

 of each spine forms a transversely elongated condyle which fits 

 into a corresponding groove between the distal segment of one 

 radial element and tlie adjacent distal end of the next succeeding 

 proximal segment. The latter family exhibit a somewhat similar 

 method of articulation, except that in the absence of distal 

 segments the binder margin of a postero-superior process forms 

 the anterior boundary of the articular groove for reception of the 

 condylar base of the spinose fin-ray. 



From what has been said as to the articular relations of the 

 fin-rays and their supporting radial elements, it is obvious that 

 the development of spinose rays in Teleosts is one of the factors 

 concerned in the reduction of typically trisegmental elements to 

 the bisegmental or unisegmental condition. The existence of 

 trisegmental elements is always associated with the support of 

 soft multiarticulate rays, and there is not a single Teleost in 

 which such elements support spines. And even where the 

 majority of the elements are bisegmental, as in the auterior 

 dorsal fin of the Siluroids, the development of special defeusive or 

 " guard-spines " is associated with the reduction of their suppoi-ts 

 to the unisegmental type. An increase even in the size of the 

 soft rays is occasionally attended by a reduction from the tri- 

 segmental to the bisegmental condition, as may be seen in the 

 anterior elements of the first dorsal fin in several of the Cypri- 

 noids. It IS, moreover, in the anterior spinose dorsal fia of the 

 Acanthopterygian Teleosts that the reduction reaches its maxi- 

 mum, extending, as it does in whole families, to the existence of 

 simple unisegmental elements. It is nevertheless certain that 

 increase in the growth of spinose rays is not the only factor in 

 this process of reduction. The Gymnotidse have sott rays com- 

 bined with unisegmental elements. The large anterior dorsal 

 spines of the Percidse, Berycidae, and Sparidse are supported by 

 bisegmental elements, but the relatively much less massive spines 

 of the Cottidae and Mugilidae by unisegmental elements. The 

 development of spines may have been one of the factors in 

 reduction, but there is also little doubt that the increasing 

 specialization of existing Teleosts and the gradual loss of many 

 of their more primitive characters are contributory causes. 



