344 AN INTRODUCTION TO THE STUDY OF FOSSILS 



The Dipneusti are known from the Devonian to the present. 

 Dipterus and Scaumenacia are well-known Devonian genera 



f,^^^^^>.<fr2 



Fig. 146. — A restoration of a dipneustan fish, Scaumenacia ciirta Wkiteaves, from 

 the Upper Devonian of Scaumenac Bay, Quebec, a.f., anal fin ; c.f., caudal fin 

 (this is heterocercal) ; d.f. i and d.f. 2, anterior and posterior dorsal fins; /./., lat- 

 eralline (a groove lined with sensory hairs) ; pec.f., pectoral fin; pel./., pelvic 

 fin. In the last two, — the paired fins, — the flesh of the body extends far into 

 the fin ; these fins correspond to the fore and hind limbs of higher vertebrates. 

 Reduced in size. (From Hussakof.) 



(Fig. 146). Ceratodus, spread over the entire world during 

 the Triassic and Jurassic, survives at present only in certain 

 rivers of Queensland, Australia. The other living forms of 

 Dipneusti are the Lepidosiren of central South America and 

 Protopterus from tropical Africa. 



Sub-class 4, Teleostomi {Bony fishes) 



In the Teleostomi (Devonian to present) the skull and 

 shoulder girdle have many dermal bones in addition to those 

 of the internal skeleton ; many of these dermal bones enter into 

 the formation of the upper and lower jaws (whence the name 

 from Greek teleos, complete, + stoma, mouth). The entire 

 skeleton is usually more or less ossified. Fin-rays bony. Gills 

 covered by an operculum. Anus distinct from urinary and 

 genital openings. Tail homocercal except in such survivors of 

 ancient types as the sturgeon and garpike, in which it is hetero- 

 cercal. Swim bladder used merely for hydrostatic purposes, 

 not respiratory. 



