1906.] 



SELACHIAN FISHES. 



743 



any other Euselacliii, The propterygium excludes the meso- 

 pterygium from the margin of the fin. The mesopterygium is 

 small and articulates directly with the pectoral arch, and most of 

 the radials are attached to the metapterygium. In the Odontas- 

 pididse the radials are simple, of moderate length and of com- 

 paratively few segments. In the Lamnidfe (text-fig. 119, E) they 



Text-fig. 119. 



Skeleton of the pectoral fin of Mustelus (A), Fristiurus (B), Oreotolohus (C), 

 Heptranckias (D), and Carcharodon (E). (A after Thacher, B and D 

 after Gegenbaur, C and E after Haswell). 



p, propterygium ; m, mesopterygiiim ; mt, metapterygium. 



are composed of several segments, and extend to the free edge 

 of the fin ; they show a tendency to bifurcate, whilst short distal 

 intercalated cartilages are developed, recalling the structure of the 

 pectoral fin in Cladoselachus. In the Scyliorhinidae and Carcha- 



