ganoidei. 365 



Second Family — Saueodipteeid^e. 



Scales ganoid, smooth lihc the surface of the skull. Two 

 dorsal fins; -paired fns obtusely loliotc. Teeth coniecd . Caudal 

 heterocercal. 



Extinct. DiplojJterus, Megcdichthys, and Ostcolejns from 

 Devonian and Carboniferous formations. 



Thied Family — Coelacanthid^. 



Sealcs cycloid. Two dorsal fins, each supported by a single 

 two-pronged interspinous hone ; paired fins dhtnscly lobate. 

 Air-Uadder ossified ; notoehord persistent, diphyeercal. 



Extinct. Coelacantlius from carboniferous strata ; several 

 other genera, from the coal formations to the chalk, have been 

 associated with it — Undina, Graphiurus, Macropoma, Holo- 

 phagus, Hoplopygus, Bhizodus. 



FouETH Family — Holoptychiid^. 



Scales cycloid or ganoid, sculptured. Two dorsal fins ; pec- 

 torals narroio, acutely lohate ; dentition dendrodont. 



Extinct. In this family a peculiar type of dentition is 

 found — the jaws are armed with two kinds of teeth, small ones 

 serially arranged, and much larger fang-like teeth disposed at 

 long intervals. Both kinds show at their base in transverse 

 sections a labyrinthic complexity of structure, numerous 

 fissures radiating from the central mass of vasodentine 

 which fills up the pulp cavity, and sending off small rami- 

 fying branches. Genera belonging to this family are Holo- 

 ptychius, Saurichthys, Glyptolepis, Dendrodus, Glyptolaemus, 

 Glyptoipomus, Tristichopterus, Gyropty chins, Strepsodus, from 

 Devonian and Carboniferous strata. 



