ORDER GANOIDEI. 



969 



Platygnathus, from the Devonian of Scotland and Russia ; Isodus, 

 of the Irish Carboniferous ; and Peplorhi?ia, from the Trias of 

 Illinois. In Glyptolepis (fig. 903), from the European and Canadian 

 Devonian, we have a well-known form in which the dorsal fins 

 are placed more anteriorly than in Holopty chins, while the anal is 

 situated below the first dorsal, and the pelvic are consequently much 



Fig. 902. — Holoptychius nobilissimus ', from the Devonian of Scotland. A, A scale less 

 reduced. The dorsal and anal fins should be more pointed. 



more approximated to the pectoral fins. Phyllolepis, founded on 

 very thick scales, which are sometimes smooth, from the Devonian 

 and Carboniferous of Scotland, should probably be included in this 

 family, in which Dr Traquair also places the imperfectly known 

 genus Dendrodus, of the Devonian of Russia and Scotland. The 

 jaws of the latter carry a small row of marginal teeth of conical 

 form ; while in the mandible there is a second row of much larger 

 fang-like teeth, each of which has 



a distinct socket. These teeth 



Fig. 903. — Restoration of Glyptolepis ; from the Devonian of Scotland. Reduced. 

 (After Huxley.) 



are somewhat compressed, with trenchant fore-and-aft edges, and 

 have the internal structure already noticed. Colo?wdns, of the 

 British Carboniferous, and Sigmodus, of the Upper Palaeozoic of 

 northern India, should perhaps find a place in this family. 



Family Rhizodontid^e. — In the Rhizodonts the pectoral fins 

 are subacutely or obtusely lobate, the pelvic pair being usually non- 



