﻿A.CTINOFTEKTGIT. 423 



Suborder IV. CLADISTIA. 



Notochord more or less constricted and replaced by ossified 

 vertebra. Baseosts in median fins rudimentary or absent ; axonosts 

 in regular series, equal in number to the apposed dermal fin-rays. 



The di- or tri-basal character of the pectoral fins, in conjunction 

 with other features, may perhaps justify the recognition of this 

 group as a distinct order. It is represented only by the family of 

 Polypteridoe (genera Polypterus and Calamoichthys), at present 

 restricted to African rivers. No extinct types are known. 



Order IT. ACTINOPTERYGII. 



Paired fins non-lobate, having an extremely abbreviated endo- 

 skeletal portion, and the dermal rays prominent ; caudal fin abbre- 

 viate-diphycercal, heterocercal, or horaocercal. A single paired series 

 of transversely elongated rays, with or without an anterior azygous 

 element, developed in the branchiostegal membrane between the 

 mandibular rami. 



Division A. — Pelvic fins with well-developed baseosts ; median 

 fins with dermal rays more numerous than the endoskeletal 

 supporting elements ; tail diphycercal or heterocercal. 

 In the living foirnis — optic nerves not decussating but form- 

 ing a chiasma, intestine with a spiral valve. 



Suborder I. CHONDROSTEL 



Notochord more or less persistent. Axonosts and baseosts of median 

 fins in simple, regular series. Membrane-bones of pectoral arch 

 comprising a pair of infraclavicular plates. 



In all known members of this suborder there is a single dorsal and 

 anal fin, well separated from the caudal. 



Synoj)sis of Families. 



A. Ascending Series. 



Trunk elongate-fusiform ; tail he- 

 terocercal ; teeth slender, conical 

 or styliform Pal^oniscid^j (p. 424). 



