592 PEOF. T. W. BBIDaD ON THE MESIAL 



the distal segments are variable in this respect, and may either 

 be simple cartilaginous nodules {Esox), or become ossified 

 {Oyprinus, Barbus, Osteoglossum, CitJiarinus), in some (e. g. Cy- 

 prinus) from two lateral centres. 



Lateral longitudinal ridges on the outer surfaces of the 

 proximal radial segments are now generally present, as ia most 

 other Teleosts, and serve to increase the surface available for the 

 origin of the erector and depressor muscles of the fin-rays. 



In the Anacanthini, represented by the Gadidse {Gadus, Mer- 

 luccius) and the Pleuronectidse (PZewro^tec^es) , the radial elements 

 with the occasional exception of the last of the series, are biseg- 

 mental, mesial segments being invariably wanting. The persist- 

 ence of simple nodular distal segments, usually cartilaginous, 

 throughout the series, even in the anterior elements, is evidently 

 associated with the absence of spinose fin-rays. In the Gradidse 

 the proximal segments possess well-developed postero-superior 

 processes in the dorsal and postero-inferior processes in the anal 

 fin, with the usual articular relations with the distal segments and 

 with contiguous proximal segments. In the Pleuronectidae these 

 processes are wanting, the proximal segments being in simple 

 parallel apposition. 



In the Acanthopterygian Teleosts, as might be expected, there 

 is a wide range of variation in the condition of the radial elements. 

 The only families in which the trisegmental type occurs are the 

 Berycidse {Solo centrum), Percidae {Mesoprion), and the Sphyrse- 

 nidae {Sphyrcena). In Solocentrum, all the ray-bearing elements 

 of the posterior non-spinose section of the dorsal fin, and, with 

 the exception of the first three, all those of the anal fin are tri- 

 segmental. In Sphyreena only the last five of the soft portion 

 of the dorsal fin and the last four of the anal fin are triseg- 

 mental ; aad in Mesoprion the last four of the posterior dorsal fin 

 and the last three of the anal fin. The remaining elements of the 

 posterior dorsal and the anal fins of the last two genera and the 

 first three of the anal fin in Holocentrum are bisegmental, as also 

 are those which support the anterior spinose section of the dorsal 

 fin in all three genera *. In the remaining Acanthopterygii, 



* It may be remarked that Holocentrum is a modern representative of one 

 of the oldest families of existing Teleosts ; and from this point of view the 

 fact that the radial elements of the hinder section of the dorsal fin and the 

 anal fin retain their primitive trisegmental character to a greater extent than 

 in any other living Acanthopterygii is of considerable interest. 



