The Crossopterygii 



605 



single family Ccelacanthida. In Ccelacanthus the fin-rays are 

 without denticles. Ccelacanthus granulatus is found in the 

 European Permian. Ccelacanthus elegans of the coal-measures 

 is found in America also. In Undina the anterior fin-rays are 

 marked with tubercles. Undina penicillata and Undina gulo 

 from the Triassic are well-preserved species. In Macropoma 

 (lewesiensis) the fin-rays are robust, long, and little articulated. 



FIG. 876. Undina gulo Egerton; Lias. Family Coelacanthida. (After Woodward.) 



Other genera are Heptanema, Coccoderma, Libys, Diplurus, 

 and Graphiurus. Diplurus longicaudatus was found by New- 

 berry in the Triassic of New Jersey and Connecticut. 



Order Cladistia. In the Cladistia the axis of the pectoral 

 limb is fan-shaped, made of two diversified bones joined by 

 cartilage. The notochord is restricted and replaced by ossi- 

 fied vertebrae. The axonosts of the dorsal and anal are in 

 regular series, each bearing a fin-ray. The order contains the 

 single family PolypteridtE. In this group the pectoral fin is 

 formed differently from that of the other Crossopterygians, 

 being broad, its base of two diverging bones with cartilage 

 between. This structure, more specialized than in any other 

 of the Crossopterygians or Dipneusti, has been regarded by 

 Gill and others, as above stated, as the origin of the fingered 

 hand (chiropterygium) of the frogs and higher vertebrates. 

 The base of the diverging bones has been identified as the ante- 

 cedent of the humerus, the bones themselves as radius and 

 ulna, while the intervening non-ossified cartilage breaks up 

 into carpal bones, from which metacarpals and digits ulti- 

 mately diverge. This hypothesis is open to considerable doubt. 



