386 Evolution and Distribution of Fishes 



Even more exact parallelism is furnished by the Serranidae, 

 which while now largely marine, still retains more ancient 

 freshwater representatives in widely apart regions. 



The Cichlidae have already been treated in relation to 

 the Centrarchidae, but from the latter, or possibly from 

 such a serranid genus as Centrogenys, a series of marine 

 groups seem clearly derivative, which with the Cichlidae 

 have by some been united as the group Pharyngognathi. 

 For while in the Centrarchidae and Percidae the two lower 

 pharyngeal bones remain distinct, these are more or less 

 joined along the median sutural line in Cichlidae. But in 

 derivative marine families fusion gradually proceeds till a 

 solid composite pharyngeal bone results. At the same time 

 the teeth gradually change from conical and pointed to 

 rounded, then to flattened, and ultimately to close pavement 

 teeth or knobs. A commencing indication of such union 

 however is seen when one compares the serranid genus 

 Trachypoma with the closely related Centrogenys. For 

 while in the former the lower pharyngeal bones are still 

 separate, in the latter they are united. It would be of 

 interest to know as to the food and feeding habits of both. 

 These changes are explained by the fishes that bear them 

 becoming more and more modified and adapted so as to 

 crush the shells of molluscs, the bodies of which form the 

 food of the fishes. This change is seen in its most primitive 



Fig. 67. 



Fig. 



Fig. 67. Upper (a) and lower (b) pharyngeal bones of Labrus. 



Fig. 68. Upper (a) and lower (b) pharyngeal bones oiScarus; 

 complete fusion of the upper bones (a) and close aggregation of 

 the teeth is seen in the latter. 



