596 PEOF. T. W. BEIDGE ON THE MESIAL 



generally the case that two elements contribute directly or 

 indirectly to the support o£ each ray. In certain families, how- 

 ever, as the result of the suppression of both mesial and distal 

 segments, either in the entire dorsal fin or in the anterior 

 section of it, the fin-rays become disassociated from their own 

 proper elements, and are supported solely by the proximal 

 radial segments immediately posterior to those to which they 

 really belong (e. g. Blenniidse, Labridse). In only one or 

 two families (e. g. Cyclopteridse), and probably as the result of 

 degeneration, are the fin-rays exclusively supported by their own 

 proper radial elements. Evidence of the concentration of fin- 

 rays is apparent in the dorsal and anal fins of most Teleostean 

 Fishes. Thus, the first radial element of the dorsal fin in Esox 

 and Coregonus supports two rays, of which the second is, without 

 doubt, its proper ray ; in Barhus and Cyprinus it supports three 

 rays in addition to the fourth — the proper ray of this element. 

 The corret^pondiug radial element of the anal fin may also suport 

 additional rays, as may the last element of both the dorsal 

 and anal fins. In all these instances the explanation previously 

 given in the case of Amia and Lepidosteus holds good. It is 

 possible in those genera (e. g. CitJtarinus) where the first radial 

 element of the dorsal fin possesses supernumerary rays or spines, 

 and there are also vestigial elements anterior to it, that the 

 additional rays pertain to certain of the hinder yestigial elements. 



The mode of articulation of the dermal fin-rays with their 

 supporting radial elements is subject to a wide range of variation 

 in diff'erent Teleosts, and even in diff"erent portions of the same 

 fin. The more characteristic articulations are, for the most part, 

 well known to ichthyologists ; but it is nevertheless worth while 

 to summarize the part played by the difterent segments of the 

 radial elements in their formation. Briefly, it may be said that 

 the method of articulation is dependent upon (1) the size of the 

 dermal fin-rays : (2) the extent and kind of movement which 

 takes place between the rays and the radial elements ; and (3) 

 variations in the method by which similar results are produced 

 in difierent groups of Fishes. 



The simplest, and probably the more primitive method, occurs 

 in such instances where, as in Amia and Lepidosteus, Osteoglossum 

 and Murcena, the cleft base of each fin-ray merely embraces or 

 clips the distal segment of its radial element. This method 

 is characteristic of the soft multiarticulate variety of fin-ray, 

 and is sometimes to be found throughout the whole extent 



