PHARYNGEAL TEETH OF FISHES. 139 



Hydrocyon brevis has eight horny gill-rakers, which are rough 

 on the inside ; these grow between the angle and the end of the 

 hypobranchial, and there is a rudimentary one on the first epi- 

 branchial. Very small, almost rudimentary ones exist on the 

 outside of the second and third arches. The inside faces of all 

 the arches are smooth. A. patch on each side of minute villi- 



Fig. I. — Hydrocyon brevis. 



form teeth represent the upper pharyngeal teeth ; the fifth 

 branchial arch carries two triangular patches covered with 

 papillae, but teeth could not be seen or felt on them. The 

 junction of the hypo- with the basibranchials forms distinct 

 little prominences, visible in the illustration (Fig. I.). 



Macrodon trahira, the Haimara of British Guiana, has five 

 short (half the length of the gill lamina below it) toothed, horny 

 gill-rakers ; along the first cerato-branchial the hypobranchial 

 is bare of gill-rakers ; there is a teeth-bearing tubercle at the 

 angle and a couple on the epibranchial ; the upper surfaces of 

 the hypo- and epibranchial are covered with minute teeth. The 

 other branchial arches are all bare of gill-rakers or tubercles, 

 but have minute teeth on them. There are for upper pharyngeal 

 teeth a small collection of minute teeth on the head and along 

 the limb of the second and third epibranchials, the latter being 

 the stronger ; there is an absence of those distinct patches or 

 shields common in other fish. Joining the third and fourth 

 epibranchials is a broad patch of villiform teeth. The lower 



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