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Suborder IV. CLADISTIA. 
Notochord more or less constricted and replaced by ossified 
vertebrae. 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 Pohjpterus and GalcimoicJithys ), at present 
restricted to African rivers. No extinct types are known. 
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Order II. ACTINOPTERYGII. 
Paired fins non-lohate, having an extremely abbreviated endo- 
skeletal portion, and the dermal rays prominent; caudal fin abbre- 
viate-diphycercal, heterocercal, or homocercal. A single paired series 
of transversely elongated rays, with or without an anterior azygous 
element, developed in the branch] ostegal membrane between the 
mandibular rami. 
Division A .—Pelvic fins with well-clev eloped baseosts ; median 
fins with dermal rays more numerous than the endoskeletal 
supporting elements; tail diphycereal or heterocercal. 
In the living forms—optic nerves not decussating but form¬ 
ing a chiasma, intestine with a spiral valve. 
Suborder I. CHONDROSTEI. 
t 
Notochord more or less persistent. Axonosts and baseosts of median 
fins in simple, regular series. Membrane-hones 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. 
Synopsis of Families. 
A. Ascending Series. 
Trunk elongate-fusiform ; tail he¬ 
terocercal ; teeth slender, conical 
or styliform .... Paljeoxiscid^ (p. 424). 
