On the Class ijlcat ion of Teleostean Fishes. 75 



Family 5. Xiphiorhyuchidse. 



Rostrum rounded in transverse section ; teeth present ; 

 nasals widely separated from the frontals by the broad 

 ethmoid ; maxillary formed of an expanded anterior and a 

 rod-like posterior portion. 



Xiphiorhynchus of the Lower and Middle Eocene. 



XII. — The Classification of Teleostean Fishes. 

 By C. Tate Regan, M.A. 



Before proceeding to the classification of the Teleostei two 

 questions must be discussed, viz. the rank and the limits of 

 tiie group. 



I have already expressed the opinion that the true Fishes 

 are at least as distinct from the Selachians on the one hand 

 and the Batrachians on the other as any of the vertebrate 

 classes are from each other, and are equally entitled to rank 

 as a class *. The class Pisces differs from the Selachii in the 

 presence of two external nasal openings on each side ; the 

 reduction of the interbranchial septa ; the development of an 

 air-bladder or lung ; the bcny exoskeleton, typically including 

 paired nasal, frontal and parietal bones, a parasphenoid, an 

 operculum, a series of bones, post-temporal, supra-cleithrum, 

 cleithrum and clavicle, overlying the primary pectoral arch 

 and connecting it with the cranium, scales and articulated 

 fin-rays ; the development of bones in or on the visceral 

 arches, prgemaxilla, maxilla, palatine, pterygoids^ quadrate, 

 dentary, &c. ; the presence of supra-neural arches (well- 

 developed in Chondrostei and Dipneusti, less evident when 

 centra are formed). The Batrachians are separated from the 

 Pisces especially by the presence of true internal nares and of 

 A fenestra ovalis, the modification of the paired fins into penta- 

 dactyle limbs and of the hyomandibular into the stapes, and 

 the absence of endoskeletal supports and dermal rays from 

 the median fins. 



Whilst recognizing the importance of the characters which 

 distingui^ih the Pisces from the Selachii, I have hitherto 

 been so conservative as to regard these groups as sub-classes 

 only, using the name Teleostomi for the former. The groups 

 which I formerly recognized as orders of the sub-class 



* Regan, Proc. Zool. Soc. 190G, p. 724, and Biol. Centr.-Am.. Pisces, 

 p. viii (1908). 



