134 A HISTORY OF FISHES 



known as Chauliodus all the teeth take the form of long, curved 

 fangs, but the pair at the front of the lower jaw are extra- 

 ordinarily long, and in order to strike upwards effectively with 

 these the fish is obliged to throw the head sharply backwards 

 (Fig. 55b). The accompanying figures illustrate the way in 

 which, when the mouth is closed, these fangs slip up the side 

 of the snout, outside the jaws. The teeth of Chauliodus are slightly 

 barbed at their tips, but in many deep-sea fishes, as well as 

 in certain of the Sea Perches (Serranidae) and Flat-fishes 

 (Heterosomata) , the barbs are strongly developed and the teeth 

 are definitely arrow-headed. A fresh- water fish from the rivers 

 of South America known as Cynodon has a pair of very formidable 

 canines at the front of the lower jaw, but instead of slipping 

 outside the jaws when the mouth is shut these are received into 

 special deep sockets in the palate and may even penetrate the 

 upper jaw (Fig. 55a). Little is known of the feeding habits 

 of this fish, but it is clear that in order to bring the canine 

 teeth into play it must be necessary to open the mouth to an 

 extraordinary extent. 



So much for the fish-eaters. In fishes with a more mixed diet, 

 including all kinds of invertebrate animals (molluscs, crustaceans, 

 worms, and the like), and in the vegetarians, the teeth may 

 be chisel-like (incisors), blunt and crushing, slender and brush- 

 like, small and jagged, or absent altogether, according to the 

 nature of the food. This diversity in the dentition is found, 

 not only in the jaws, but also in the throat teeth and in those 

 on the roof of the mouth. In the Flounder {Flesus), for example, 

 the lower pharyngeals are united to form a triangular plate, 

 and the associated teeth are mostly in the form of bluntly 

 pointed cones, the teeth in the jaws being also conical; in the 

 Plaice (Pleuronectes) , on the other hand, most of the pharyngeal 

 teeth are blunt crushing molars and the jaw teeth chisel-like. 

 A study of the food of the two fishes shows that the Plaice 

 includes a much higher percentage of shell-fish in its diet, and 

 the crushing pharyngeal teeth are admirably suited for such 

 food. Many of the Sea Breams (Sparidae) live on a similar diet, 

 and the teeth are pointed in thefront of the jaws and molar-like 

 on the sides, being designed respectively to break and grind 

 up the shell-fish. The Wolf-fish {Anarrhichas) has a group of 

 long curved canines anteriorly in each jaw, and in the hinder 

 part of the lower jaw a double row of rounded molars: the roof 

 of the mouth is provided with three double rows, the middle 

 ones flat and those at the sides pointed. Among the Cichlids 



