282 



OSTEOLEPIDOTI 



Teleostomes (Polypterini and Actinopterygii). The extensive 

 cheek region is covered partly by the postorbitals and partly by 

 one or more large plates representing the preoperculum (Fig. 251). 

 Sometimes a normal preoperculum is present, with separate cheek- 

 plates in front (Fig. 256). A row of three supratemporal plates 

 covers the occipital region. 



The lower jaw is provided, as a rule, with a series of infra- 



dentaries. On either side of 

 the large paired inferior gular 

 plates a series of lateral gulars 

 extends upwards to the sub- 

 opercular and opercular bones 

 (Fig. 250). The interoper- 

 cular has not been identified 

 for certain. The anterior 

 median gular, if present, is 

 small. On the inner side 

 of the mandible, the splenial 

 bears large teeth, and may 

 be subdivided into several 

 ossicles. Large teeth are 

 also present above in the 

 vomerine and palatine regions. 

 The wall of these teeth tends 

 to become much folded 

 (p. 285). 



The paired fins have an 

 outstanding scale-covered lobe 

 of considerable size. In some 

 (Holoptychiidae) this central 

 axial region is elongate and 

 tapering, 'acutely lobate,' with 

 a fringe of lepidotrichia on 

 FIG. 252. either side, thus closely re- 



A, en.loskeleton of the second dorsal fin of Sembling the fin of CeratoduS 



Glyptokpis leptojitei-iis, Ag. B, skeleton of the left /]?: 9^X\ TTnfnrtnnarplv 



pectoral lin of Em>thenvpteronVoonn,\{\\t.; restored. V rl - ^Ot). U n] tel y> 



, segment of longitudinal axis ; a.b, basal segment the internal skeleton is UU- 

 of axis ; 6, basal; d.r, dermal rays; p.p, postaxial . . 



process (radial?); pr.r, preaxial radial ; r, radial. known in these forms ; but it 



would appear to have been 



built on the mesorachic plan, with a jointed central axis bearing 

 preaxial and postaxial radials. In the Osteolepidae the fins, especi- 

 ally the pelvics, are shorter, and less acutely lobate ; in these also 

 the endoskeleton is unknown. The Rhizodontidae have lobate fins- 

 departing from the mesorachic type : here the preaxial edge and its 

 dermal rays are becoming stronger than the postaxial, as in the 

 Actinopterygii, while the skeletal axis is somewhat posterior (Fig, 



\N< . ? 



V v N 



prr. 



Wi llfe 



! ' >\\\\V\^v ' 



dr. 



