2 7 8 



TELEOSTOMI 



and Teleostei, placing two orders in the former, the Holostei 

 (Lepidosteus and Polypterus) and the Chondrostei (Acipenserini and 

 Spatulariae). Thus was laid the foundation of our modern classifica- 

 tion. Miiller's Ganoidei are distinguished from the Teleostei by 

 the possession of a valvular contractile conus, a spiral valve, and an 

 optic chiasma. C. Vogt [474^] subsequently showed that Amia 

 belongs to this group. 



The next great step was made by Huxley [227]. Treating the 

 fossil in conjunction with the living fish, he subdivided the 

 Ganoidei into Amiadae, Lepidosteidae, Crossopterygidae, Chon- 

 drosteidae, and Acanthodidae. The foundation of the group 

 Crossopterygidae was a great advance, for in it were gathered 



together with Polypterus a 

 number of related but hitherto 

 scattered genera clearly dis- 

 tinguished from the remainder 

 of the Ganoidei. On- the 

 other hand, the work of Cope, 

 A. S. Woodward, and others 

 on extinct fish has tended to 

 break down the distinction 

 between the Ganoidei and 

 Teleostei. It is now coming 

 to be recognised that none of 

 these older classifications is 

 strictly in accordance with 

 a phylogenetic scheme. 



The reunion of the Amia- 



Ventaalview of the pelvic girdle and fins of dae > Lepidostcidae, and Choil- 



Gadus morrhua, L. d.r, dermal rays (lepidotrichia) ; drOSteidae into the One 2TOUD 



m.c, median cartilage ; p, pelvic bone; posterior , .. , ^ Y~ , n 



process. (From Quart. Jmtrn. M icr. Sci.) Actmoptcrygll by Cope [91J 



was the next important move 



towards a more natural classification. But the Crossopterygidae 

 of Huxley, the only common and diagnostic character of which 

 is the possession of a pair of large gular plates, tend now 

 to fall apart into a number of diverging groups whose mutual 

 affinities are very doubtful. The Dipnoi have been separated off 

 as a specialised offshoot, related to but probably not derived from 

 any known Osteolepidotid (p. 258). It is true that the Crosso- 

 pterygidae have more or less ' lobed ' paired fins fringed with dermal 

 rays, but so have many other fish; and the supposition that the 

 endoskeleton of these fins has been derived from the rachiostichous 

 and mesorachic type found in Dipnoi rests on speculations which 

 are neither firmly established nor generally accepted (p. 282). 



The Teleostomi, as originally defined by Owen, included the 

 Gtanoidei, Dipnoi, and Teleostei. We now use the term in a more 



