THE PHARYNGEAL TEETH OF FISHES. 183 



POLYPTEKIDiE. 



Polypterus senegalus, a fish found in the rivers of West Africa. 

 A few flat, tubercular patches with very fine villiform teeth on 

 the outer and inner sides of the first three arches represent all 

 that this fish has for gill-rakers. There are no pharyngeal 

 teeth (fig. III., 1). 



AciPENSERID^E. 



Acipe?iser sturio, the Sturgeon, has twelve short, horny gill- 

 rakers on the first cerato-hypobranchial, with six on the 

 epibranchial. They are placed low down on the outside of the 

 arch instead of standing on the upper edge. The longest is one- 

 fifth of the depth of the gill-laminaa below it ; these gill-rakers 

 stand up distinctly apart from each other. The inside of the 

 first arch, and both sides of the second, third, and fourth arches, 

 have short, upstanding, horny gill-rakers much more numerous 

 than those on the outside of the first arch, the inside of this 

 having twenty-two gill-rakers ; they are, however, less broad in 

 structure, and stand out like a row of little pegs. There are no 

 pharyngeal teeth. 



Ceratodontid^;. 



Neoceratodus forsteri, a fish that breathes by lungs as well as 

 by gills, is found only in two or three rivers of Queensland, 

 Australia, and said to be getting extinct there. It is called locally 

 the " Flat-head," also " Burnett " or " Dawson " Salmon, accord- 

 ing to the river in which it is caught. It has sixty-two short, 

 fleshy gill-rakers from the extremity of the first epibranchial to 

 the end of the first hypobranchial. The angle not being clearly 

 defined, the total number is noted. The longest are only 

 one-tenth of the depth of the gill-laminse below them. There 

 are forty-two similar gill-rakers on the inside of the hyoid bone, 

 shown opened back in the illustration. There are similar gill- 

 rakers on each side of the gill-slits, those on the inner sides 

 being longer than those on the outside. The upper surfaces of 

 the arches are covered with fleshy papillse of a bluntly-pointed 

 shape, those on the first arch being triangular. At the junction 

 of the hypo- with the basibranchial are bigger, broader, but still 

 pointed papillse. The upper back part of the gullet is marked 

 with corrugations that fit over the gill- slits, and the whole 



