NO. 3 



TELEOSTEAN FISHES GOSLINE 



15 



the postterminal centra have fused with the terminal vertebra to 

 form a tapering point (urostyle) on the latter; there is only a single 

 uroneural (which is not fused to the terminal vertebra) ; there are 3 

 epurals and 6 hypurals ; and the first preterminal vertebra bears a 

 neural crest but no neural spine. 



In contrast to Antigonia, the caudal skeleton of Zeus (cf ., Norman, 

 1934, p. 6, fig. 6D) has undergone so much fusion that its component 

 parts are identifiable only with difficulty. 



Fig. 4. — A, Caudal skeleton of Antigonia capros (Zeiformes). Lettering as 

 in figure i, A. 



B, Caudal skeleton of Epinephelus bonaci (Perciformes). 



With regard to the Perciformes, the only point that will be made 

 here has to do with two presumably derivative groups, namely, the 

 Mugiloidei (Percesoces) and the Pleuronecti formes (Heterosomata). 

 In both of these (cf., Hollister, 1937a, and Norman, 1934, p. 3, fig. 3, 

 respectively) the caudal skeleton shows considerably more fusion than 

 in the basal percoids (fig. 4B). 



Discussion. — Three matters will be taken up here : the sequence in 

 the fusion of parts of the caudal skeleton; the similarities in structure 

 shown by the basal members of various groups; and finally the evolu- 

 tionary changes that have occurred in the caudal skeleton within 

 groups. 



At the different levels of organization between the isospondylous 

 fishes and the percoids there has been a progressive reduction in the 

 number of parts. Some of this has doubtless come about through loss, 

 but perhaps a greater portion has been the result of fusion. The ex- 



