126 



FISHES. 



without an angular bent near their base ; some are compressed 

 laterally or from the front backwards ; the latter may be 

 triangular in shape, or truncated at the top like incisors of 

 mammals ; they may have one apex (cusp) only, or be bi- or 

 tri-lobate (bi- or tri-cuspid) ; or have the margins denticu- 

 lated or serrated. Compressed teeth may be confluent, and 

 form a cutting edge in. both jaws, which assume the shape 

 of a parrot's beak (Fig. 53). In some the apex is hooked 



or provided with barbs. 

 Again, some teeth are 

 broad, with flat or convex 

 surface, like molar teeth. 

 With regard to size, the 

 finest teeth are like fine 

 flexible bristles, ciliiform 

 or setiform ; or, if very 

 short and anchylosed to 

 the bone, they appear 

 only as inconspicuous asperities of the bone. Very fine conical 

 teeth arranged in a band are termed villiform teeth ; when 

 they are coarser, or mixed with coarser teeth, they are card- 

 like (dents en rape or en cardes) (Fig. 54) ; molar-like teeth 

 of very small size are termed granular. 



In all fishes the teeth are constantly shed or renewed 

 during the whole course of their life. In fishes which have 

 compound teeth, as the Dipnoi, Chimseroids, Scari,^ Gym- 

 nodonts, as weU as in those which have apparently permanent 

 teeth, as in the saw of Pristis, the detrition of the surface is 

 made up by a constant growth of the tooth from its base. 

 When the teeth are implanted in alveoli, they are generally 

 succeeded by others in the vertical direction, but in others 

 they succeed one another, side by side. In the majority of 



' On the development and structure of the dentition of Scarina, see Boas, 

 "Die Zsihne der Scaroiden," in Zeitschr. f. Wiss. Zoolog. xxxii. (1878). 



Fig. 53. — Jaws of Calliodon. 



