NO. 3 TELEOSTEAN FISHES — GOSLINE 1 7 



tionary side lines. It thus seems more probable that the representa- 

 tives of these types are either phylogenetically related or have evolved 

 their caudal similarities as the results of rather unusual environmental 

 stresses (or both). The (Type II) resemblances between the round 

 herrings and the characin Brycon are particularly intriguing in this 

 regard, for the similarities extend to trivialities. 



As to Type III, it is difificult to understand why postterminal 

 vertebra 2 should have fused with upper hypurals in such divergent 

 fishes as osteoglossoids, the Percopsi formes, cyprinodonts, Velifer, 

 and apparently in eels. Perhaps the best explanation that can be 

 offered is that suggested in a previous paper (Gosline, i960), namely, 

 that these forms have all had round-tailed ancestral forms, even if 

 they have a forked tail now. Of these groups the caudal skeletons of 

 only Aphredodorus and Amblyopsis show sufficient similarity in detail 

 to suggest an inquiry into the possibiHty of phylogenetic relationship. 



In the introduction to the paper the within-group evolution of the 

 structures dealt with was noted. Since the caudal skeleton shows this 

 feature the most strikingly of the four characters examined, the sub- 

 ject will be discussed here. 



Our present classification of teleostean fishes has been erected 

 chiefly through efforts to distinguish groups, and for purposes of 

 presentation the "orders" are frequently represented as a series of 

 beads attached to one another by longer or shorter strings. As a re- 

 sult, the fact that evolution has occurred within orders has become 

 obscured. 



Now it is very possible that the major teleostean orders originally 

 did evolve in response to a particular mode of life (Simpson, 1944), 

 and that if only the characters involved in these adaptations are con- 

 sidered, the orders could be represented as a series of rather separate 

 beads. Nevertheless, such characters would only represent a very 

 small proportion of those found in the fish as a whole. For all other 

 features progressive change would either not occur or might be ex- 

 pected as much within as between orders. As far as the caudal 

 skeleton is concerned, the amount of change that takes place within 

 the ostariophysine fishes and other orders is far greater than the 

 difference between Alhiila and Epinephelus. Or, to put the matter 

 differently, the caudal skeletons of the basal berycoids and serranids 

 are nearer the basal clupeiform type than that of Clupea. 



II. SOME FEATURES OF PELVIC STRUCTURE 



The position of the pelvic fin and the number of its rays are almost 

 universally used in the higher classification of teleostean fishes. In- 



