238 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



sphenoid. Second suborbital not forming a stay for the praeoperculum. Posttemporal 

 more or less distinctly forked." 



These of course are merely the characters selected by systematists for the construction 

 of convenient keys for "running down" the taxonomic position of a given specimen. But 

 they are mere isolated fragments of the typical percomorph skeletal pattern, which happen 

 to be easily recognizable in at least most of the members of this large and highly diversified 

 assemblage and to be useful in excluding from the central group many of its own derivatives. 



In this chapter we show a few skulls of representatives of this many-branched stock. 

 In the most primitive members of the series the body is short and comparatively deep with 

 only twenty-four vertebrae, recalling the conditions in the ancestral berycoids, but in many 

 more advanced forms the body becomes more or less elongated while the vertebrse increase 

 in number. The shape of the head as a whole is closely correlated with the general body- 

 form, or to put it more precisely, each one is correlated with the other, so that the skulls 

 pass from relatively short and deep to long and shallow contours. The contours are so ad- 

 justed to each other that the "angle of entrance" is greater than that of the "run" or 

 tapering part of the body. 



p+0 

 CS.t> 



SOC ^J 



defh parefK 



•pel 



pelv 



^. Micropterus dolomieu 



Fig. 113. Micropterus dolomieu. 



In Micropterus dolomieu (Fig. 113) a progressive member of the family Centrachidae, 

 the skull may be regarded as near the central percoid type. The distance between the 



