458 MR. C. TATE REGAN ON THE 



If only the living forms wei^e considered, it might be held that 

 the Ohondrostei, Holostei, and Teleostei were groups of equivalent 

 rank- Bat a study of the fossils shows that this conclusion is 

 wrong. . The mesozoic Pholidophoridse and Oligopleuridfe resemble 

 the Holostei in the structure of the caudal fin (and in the 

 PhoHdophoridae of their scales), but in other characters, such as 

 the small loose prsemaxillaries, the maxillary with convex oral 

 edge and bearing two supramaxillaries *, and the absence of a 

 " supra-angular," they show clear evidence of their relationship 

 to the Elopidse. 



The Pholidophoridse had minute teeth, and were probably 

 plankton -feeders like the Herrings, which they resemble in form 

 and in the shape of the fins. They are evidently another off- 

 shoot of the Semionotidee, from which they differ especially in the 

 structure of the mouth, and they lead to the Leptolepidse and 

 Elopidae. These are stronger swimmers, with a deeply-forked 

 caudal fin, in which the upper hypurals are for the first time 

 supported by uroneurals, paired bones that I'eplace the uptui-ned 

 end of the vertebral colvimn. 



The Holostei and Teleostei, therefore, are one group, for 

 which it seems better to use the name Neopterygii, rather than 

 to use Holostei or Teleostei in a new and extended sense ; 

 whilst the name Paleeopterygii may be u,T!ed to designate the 

 group including the Palaeoniscoids, Ohondrostei, and Belono- 

 rhynchii. 



I have long considered that the Selachians constitute a distinct 

 class {cf. P. Z. S. 1906, p. 724), and if that be admitted, the main 

 groups of the Pisces t may be termed subclasses. These are six 

 in number — namel}' Palgeopterygii, JSTeopterygii, Cladistia, Rhipi- 

 distia., Actinistia, and Dipneusti, the probable relationships of 

 which are indicated in the following scheme : — 



Actinistia. Dipneusti. 



Cladistia. Rhipidistia. 

 Neopterygii. 



Pala3opterygii. 



The Neopterygii are defined by the dorsal and anal fins with 

 pterygiophores equal in number to the dermal rays, the absence of 

 clavicles and of paired gulars, the presence of an interoperculum, 



* It is worth noting that one supramaxillavy and a supra-angular, and two supra- 

 maxillaries and no supra-angular are alternative conditions, almost suggesting that 

 the maxillar3'^ has captured the supra-angular from the lower jaw. But it seems more 

 likely that the supra-angular has gone, and that as the maxillarj'- lengthened another 

 suborbital has become attached to it. 



t I exclude from the Pisces a nvnnber of Palaeozoic groups of uncertain relation- 

 ships, e. (/. Arthrodira, Asterolepida, Osteostraci, etc. 



