86 TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



10. Typical percomorph (Fig. 114); outer bones sunk beneath surface of skin and often 

 more or less pitted along lateral line tracts; endosteal and ectosteal bones of braincase and 

 mandible tending to lose separate identity; premaxillse protrusile, excluding maxillae from 

 oral border; maxillae serving as levers for depression of alveolar bar of premaxilla; one 

 supramaxilla (except in the most primitive berycoids); mandible without "splenial" (coro- 

 noid) elements; typically six branchiostegals, of which four are attached to the epi- and 

 cerato-hyal (Hubbs); orbitosphenoid absent, basisphenoid much reduced; supraoccipital 

 forming a large median keel and in contact with frontal; occipital condyles tripartite. 

 Upper Cretaceous. 



Stages 5-10 of this outline of the evolution of the teleost skull are in conformity with 

 those given by Smith Woodward in 1895, but have here been independently described and 

 checked against the material. 



Thus a typical percomorph syncranium as a whole appears rather widely different 

 from that of a primitive palseoniscoid ganoid, yet, as we have seen, the number of important 

 morphological differences between them is much less than the number of fundamental 

 agreements. 



Diagrams showing a tentative summary of the phylogeny of the principal groups of 

 fishes from the ostracoderms to the most highly specialized teleosts are given in Plate II. 



