140 ORDERS OF FISHES. 



or stem, which is covered by scales, and to the sides of which 

 the fin -rays are attaclied. Tlie nearest approach to this 

 structure amongst living fishes is found in the paired fins of 

 the Barramunda {Ccratodus Forsteri) of the rivers of Queens- 

 land. In this singular fish, which is referable to the order 

 of the Dipioi, the pectoral and ventral fins are supported by 

 a median, many-jointed, cartilaginous rod, to which numerous 

 lateral branches are attached (fig. 489). The scales in this 

 sub -order are sometimes rhomboidal, not overlapping one 

 another ; at other times they are cycloidal in shape, and are 

 arranged in an imbricate manner. 



Professor Huxley, in his classical memoir upon the Fossil 

 Ganoids, divides the Crosscrptcrygidm into the following fam- 

 ilies {see ' Memoirs of the Geological Survey of Great 

 Britain. Decade X.') : — 



Fain. 1. — POLYPTERINI. 



Dorsal fin very long, niultifid ; scales rhomboidal. 

 Polypterus (fig. 500). 



Fani. 2. — Saurodipterini. 



Dorsal fins two ; scales rhomboidal, smooth ; fins sub-acutely 

 lobate. 



Diplopterus, Osteolepis (fig. 500), Megalichthys. 



Fani. 3. — Glyptodipterini. 



Dorsal fins two ; scales rhomboidal or cycloidal, sculptured ; 

 pectoral fins acutely lobate ; dentition dendrodont. 

 Sub-fam. A. with rhomboidal scales. 



Glyptolcemus (fig. 506), Glyptopomus, Gyroptychius. 

 Sub-fam. B. with cycloidal scales. 



Holoptychius (fig. 507), Glyptoleins, Platygnatkus [Rhizodus, 

 Dendrodus, Cricodus, Lamnodus], 



Fam. 4. — Ctenodipterini, 



Dorsal fins two; scales cycloidal ; pectorals and ventrals acutely 

 lobate ; dentition ctenodont. 



Dipterus \Ceratodus f Tristichopterus .?! 



Fam. 5. — Phaneropleurini. 



Dorsal fin single, very long, not subdivided, supported by many 

 interspinous bones ; scales thin, cycloidal; teeth conical, ven- 

 tral fins very long, acutely lobate. 

 Phaneropleuron (fig. 510). 



