PHYLOGENY. 



103 



bones ^ in the fins of families whicli have pectoral ven- 

 tral fins, and in the extinct genus Dorypterus.^ 



The Malacopterygia display three or four distinct 

 lines of descent. The simplest type is represented by 

 the order Isospondyli, and paleontology indicates clearly 

 that this order is also the oldest, as it dates from the 

 Trias at least. In one line the anterior dorsal verte- 

 brae have become complicated, and form an interlock- 

 ing mass which is intimately connected with the sense 

 of equilibrium in the water. This series commences 

 with the Characinidae, passes through the Cyprinidae, 

 and ends with the Siluridae. The arrangements for 

 equilibration constitute a superadded complication, 

 and to these are added in the Siluroids defensive spines 

 and armor. Some of this order, however, are distinctly 

 degenerate, as the soft purblind Ageniosus, and the 

 parasitic Stegophilus and Vandellia, which are nearly 

 blind, without weapons, and with greatly reduced fins. 



The next line (the Haplomi, pike, etc.) loses the 

 precoracoid arch and has the parietal bones separated, 

 both characters of the Acanthopterygia. This group 

 was apparently abundant during the Cretaceous period, 

 and it may have given origin to many of the Acantho- 

 pterygia. 



Another hne also loses the precoracoid, but in other 

 respects 'diverges totally from the Acanthopterygia and 

 all other Malacopterygia. This is the line of the eels. 

 They next lose the connection between the scapular 

 arch and the skull, which is followed by the loss of the 

 pectoral fin. The ventral fin disappeared sooner. The 

 palatine bones and teeth disappear, and the suspensor 



ISee Cope " On the Homologies of the Fins of Fishes" ; American Nat- 

 uralist, i8go, p. 401. 



2 See Proceedings of the American Association for the Advancement of Sci- 

 ence, 1878, p. 297. 



