FINS. 



23 



less than seven supports are fused into one mass, and remnants 

 of a still greater number are clustered together distally. The 

 process is again observed to some extent in the anal fin of the 

 Dipnoan Scaumenacia (fig. 20). In the Ccelacanthidae (fig. 60, 

 p. 80) the distal cartilages (baseosts) of the hinder dorsal fin 

 are too little calcified to be preserved, while those of the 

 anterior dorsal fin have entirely disappeared and the dermal 

 rays are in direct contact with the compound triangular base 



A. 



B. 



FIG. 21. 



Cladoselache ; pectoral (A) and pelvic (B) fins, one-half nat. size. U. Devonian ; 

 Ohio. B, basal cartilages within body-wall ; D, dermal fin-membrane ; 

 B, endoskeletal cartilaginous rays. Left border preaxial, right border post- 

 axial. (After Dean.) 



(axonost). The Coelacanths are certainly a more specialized 

 group than the Holoptychiidae and are all of later date ; hence, 

 since the type of dorsal fin they exhibit has never been found 

 among the Crossopterygian contemporaries of the Holopty- 

 chiidye, it is evident that crowding and fusion of the supports 

 take place first, shortening next. Parenthetically, it may be 

 added that when subdivision of the dorsal fin occurs in this 

 manner, it invariably results in two small fins, never more or 

 less. 



