PHARYNGEAL TEETH OF FISHES. 



389 



teeth, and on the fourth a patch of strong conical teeth. The 

 lower pharyngeals are in a triangular patch. The bones of the 

 fifth arch are united. 



Hemichromis bimaculatus, a Nile fish, has five gill-rakers on 

 the first cerato-hypobranchial, with two on the epibranchial of 

 the first arch. The upper and lower pharyngeal teeth are 

 minute cardiform ones of a dark colour. 



Tilapia nilotica, a Nile fish, has twenty-two soft but up- 

 standing gill-rakers on the cerato-hypobranchial part of the first 

 arch, with six on its epibranchial. The inside of the first arch 

 and both sides of the other arches have gill-rakers that fit in 



Fig. IV. 

 1. — Sebastes imperialis. 2. — Balistes capriscus. 3.— Tilapia nilotica. 



opposite to each other so closely as to make a very efficient 

 filter. The upper pharyngeal teeth are placed in two oval- 

 shaped shields on each side, and are cardiform teeth of a blackish 

 brown colour, the multiplicity of fine points giving the whole 

 shield of teeth a dusky hue. The lower pharyngeal teeth are in 

 a triangular patch across the whole floor of the gullet just in 

 front of the oesophagus, with no median division ; the dark 

 colour, however, is not so marked as in the upper pharyngeal 

 teeth, those toward the forward apex merging into white. The 

 base of the tongue and the mucous surface of the basibranchials 

 is worked with corrugations in pattern like the veining of some 

 leaf. Fig. IV., 3. 



(To be continued.) 



