98 



Crossopterygii. 



ORDER I. Crossopterygii. 



Wall-cases - finned fishes, or Crossopterygians, are now 



Nos. 5 to 7,' almost extinct, being represented only at the present day by 

 and Table- ^ Polypterus (Fig. 136) and Calamoichthys of the African rivers, 

 case, o. o. j n ^ Q j) evoll i an an( j Carboniferous periods they existed in 



FIG. 136. Polypterus Mchir, living in the Nile, Gambia, etc. 

 a, pectoral fin; 6, pelvic tin; c, anal fin. 



large numbers and in much greater variety. HoloptycJiius (Fig. 

 137) is an Upper Devonian genus from Scotland and Russia, 

 with long and acutely- lobate pectoral fins, obtnsely-lobate pelvic 



&fc 



FIG. 137. Holoptychius ; U. Old Red Sandstone, Fifeshire (restored by Huxley), , paired 

 pectoral fins ; b, pelvic tins ; c, the anal fin ; d, anterior dorsal fin ; e, posterior dorsal fin. 



fins, and thick, round, deeply overlapping scales. Glyptolepis, 

 from the Lower Old Red Sandstone of Scotland, and apparently 

 from the Upper Devonian of Canada, is a nearly identical 

 genus. Glyptolcemus (Fig. 138), from the Upper Old Red Sand- 

 stone of Dura Den, Fifeshire, has more obtuse pectoral fins and 

 rhombic scales. Osteolepis (Fig. 139), Diplopterus, Tkursius 

 (Devonian), and Megalichthys (Carboniferous and Lower Per- 

 mian) are another group of genera with enamelled rhombic 



FIG. 138. Glyptolamus Kinnairdi, Huxl. (restored by Huxley) ; U. Old Red Sandstone, 



Scotland. 



