2794 



THE BONY FISHES AND GANOIDS 



variable in form, is generally covered with ctenoid scales, although in some cases 

 these may be cycloid; and the lateral line is more or less interrupted. In the single 

 dorsal fin the spinous portion usually exceeds the soft in extent; the anal fin 

 having three or more spines, and its rayed portion being similar to the soft dorsal. 

 The jaws are provided with small teeth, but the palate is smooth; and the number 

 of gills is four. In some species the teeth are lobate and the intestines complicated 

 by many foldings; these types being vegetable feeders while all the remainder are 

 carnivorous. Among the best-known representatives of the typical genus Chromis 

 is the so-called butti of the Nile (C. niloticus}, which is one of the largest members 

 of the family; while Tristram's chromid (C. tristrami} here figured is from salt and 

 other lakes in the Sahara and Ashanti. As a genus, Chromis is distinguished by 

 its lobate teeth, the presence of only three spines in the anal fin, and the scaly gill 



I 





TRISTRAM'S CHROMID. 



cover; and it therefore belongs to the vegetable-feeding group. Nineteen existing 

 genera have been described; and the family appears to be represented by one, or 

 perhaps two extinct generic types from the middle Eocene of Monte Bolca, in Italy. 



THE TuFT-GILIvED AND COMB-GILLED FlSHES SUBORDERS 

 Lophobranchi and Plectognathi 



The two small subordinal groups of fan-finned fishes now to be noticed have 

 been generally placed after the soft-finned fishes, but from recent investigations 

 into their anatomy it appears more probable that they are highly specialized types 

 related to the spiny-finned group. 



