GANOIDEI. 365 



Second Family — SAURODiPTEEiDiE. 



Scales ganoid, smooth like the surface of the shall. Two 

 dorsal fns; paired fns ohtuselylobate. Teeth conical. Caudal 

 heterocercal. 



Extinct. Diplopterus, Megalichthys, and Osteolepis from 

 Devonian and Carboniferous formations. 



Third Family — CoELACANTHiDiE. 



Scales cycloid. Ttvo dorsal fins, each supported hy a single 

 two-pronged interspinous lone ; paired fins oltusely lohate. 

 Air-hladder ossified; notochord persistent, diphycercal. 



Extinct. Coelacanthus from carboniferous strata; several 

 otter genera, from the coal formations to tlie chalk, have been 

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

 phagus, Sopl(ypygus, Bhizodus. 



EouETH Family — HoLOPTYcmiDiE. 



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

 torals narrow, acutely loiate ; 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 kiads show at their base in transverse 

 sections a labyrinthic complexity of structure, numerous 

 iissures radiating from the central mass of vasodentine 

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

 fjdng branches. Genera belonging to this family are Holo- 

 ptychius, Saurichthys, Ghjptolepis, Dendrodus, Glyptolaemus, 

 Glyptopomus, Tristichopterus, Gyroptychius, Strepsodus, from 

 Devonian and Carboniferous strata. 



