322 KDVVIN S. GOODUIOH. 



some cases, however, as in Dipnoi and Teleosts, they are well 

 differeutiated; in other cases, as in the Chondostrei, they are 

 ill-defined, and probably in a more or less degenerate con- 

 dition, not clearly marked ott" from the true fin skeleton. 



To conclude, we may briefly mention the evidence afforded 

 by the structure of the skeleton of the pelvic fin as to the 

 systematic position of Eusthenopteron. Unfortunately Ave 

 know hardly anything about the structure of the fin skeleton 

 of other extinct " Crossopterygii." But from our know- 

 ledge of the Dipnoi, it may be inferred with some degree of 

 certainty that the skeleton ot the elongated lobed fins of 

 such forms as Griyptolepis and Osteolepis was built on the 



Fig. L. — Ventral view of the pelvic girdle and fins of Holophagus gulo, 



Huxley. 



biserial archipterygial plan (distichopterygia). It is there- 

 fore of considerable interest to note that although in the 

 shape of the outline of the fin-web, and in the disposition 

 and structui-e of the dermal rays, the pelvic limb of Eus- 

 thenopteron approximates to that of the more highly 

 specialised Teleostomes (Actinopterygii) ; yet its internal 

 skeleton is probably to be interpreted as a modification of 

 the biserial archipterygium, with a distinct axis, in which 

 the post-axial endo-skeletal rays have been lost. Further, 

 the skeleton of the pectoral and of the pelvic fin of Eusthe- 

 nopteron still exhibit that close resemblance to each other 

 which is so marked a characteristic of the Dipnoan fins, and 

 presumably also of the more pi-imitive forms from which they 

 have been derived. 



In contrast to this we find in Polypterus and the Actinop- 



