GREGORY. PRESENT STATUS OF ORIGIN OF TETRAPODA 361 



jjarison with Sauripterus a figure of an American Museum specimen re- 

 ferred to Osteolepis microlepidotus, showing the head, shoulder-girdle 

 and pectoral fin (Fig. 10). 



Further consideration compelled me (1912, p. 220) to give up the 

 idea that the ascending blade of the shoulder-girdle in Rhipidistia repre- 

 sents the scapulocoracoid of Tetrapoda, partly because the type of Saurip- 

 ierus taylori retains a portion of an element that lies between the ascend- 

 ing blade and the "humerus" or single proximal piece. The rest of this 

 element probably covered a part of the medial surface of the dermal 

 ascending blade and may have been present in the counterpart of the 



Fig. 10. — Head and pectnnil limh of OHteoU'jJis inici oleijidottis 



Crushed specimen in tine American Museum (No. 7715). Slightly less than natural 

 size. The massive cleithrum is partly overlapped by the operculum and suboperculura. 

 The pectoral fin shows the large scales or plates covering the "humerus," the elongate 

 plate covering the postaxial element, or "radius," the scales on the fleshy part of the 

 fin and the dermal rays. 



type, which was not obtained. In Ceratodus (Fig. 5) a corresponding 

 piece is apparently homologous with the scapulocoracoid element of tetra- 

 pods, which is of course a cartilage bone. I therefore return to Gegen- 

 baur's view (1895), which is also that of Dr. Broom, that the ascending 

 blade in Sauripterus represents the cleithrum of primitive Stegocephali, 

 although in them it is much reduced and the scapulocoracoid correspond- 

 ingly enlarged. Accordingly the homologies of the elements of the 

 pectoral limb in Rhipidistia and primitive Tetrapoda (F\^. 11) appear 

 to be as follows : 



RHIPIDISTIA 



Interclavicular corium 

 Clavicle ("infra clavicle") 

 Supracleithriim ( "supraclavicle" ) 



Post-temporal 

 Coracoscapula 



TETRAPODA 



Inter clavicle 



Clavicle 



? Fused with top of cleithrum 



Sclerocephalus) 

 Lost 

 Coracoscapula 



(c/. 



