8 THE CYPRINODONTS. 



depressed in Anableps, and to much compressed in Cyprinodon and others. 

 In all species the caudal region is compressed. The head and cheeks are 

 covered with scales. The gills, four in number commonly, are well pro- 

 tected. Those forms subjected to the roughest treatment, from rocks or 

 currents, as Anableps, have the walls of the gill-chamber of more than 

 ordinary firmness. Pseudobranchite occur in few cases. The scales are 

 comparatively large and firm ; on Rivulus they are thin, and on Orestias, 

 with age they become thick and tubercular on some portions of the body 

 and head. 



With the variety in habits there are great differences in structure. Such 

 are particularly noticeable in the mouth. Generally the intermaxillary forms 

 the upper border of the mouth and is dentigerous. Among those forms in 

 which the mouth is most protractile the internarial processes of the inter- 

 maxillaries are narrow and elongate ; but in species like Cyprinodon these 

 processes are short aiad broad. Beloneso.x and Haplochilus have the inter- 

 maxillaries produced forward so that the snout is shovel-shaped. Ordinarily 

 the upper jaw is narrow at the angle of the mouth ; Nothobranchius has a 

 mouth more like a perch. The mandibles of many are firmly joined at the 

 symphysis ; but in Poecilia and allies the connection is very loose. Excep- 

 tional species of Haplochilus have vomerine teeth. On Plates I. to V., 

 the teeth of many of the genera and species are shown. The variations 

 range from the simple conical firmly set teeth of Haplochilinoe to the com- 

 pressed tricuspids of Cyprinodon, or to the broad oar-shaped movable ones 

 of Pcecilire. The number of series varies from one to many. Funduloids 

 usually have on each jaw a series of larger teeth behind which there are 

 several series of smaller ones in a viliform band. There are African species 

 which have two series of larger ones to each jaw, and between them a band 

 of smaller ones. The pharyngeal teeth vary nearly as much as those of the 

 mouth. In some they are simple conical hooks; in others they have a shoul- 

 der, more or less blade-like, below the hook ; and in still others, some or 

 nuiny of the teeth lose the cusps and enlarge to become stout, broad- 

 crowned molars. These teeth are rigidly set in most cases, but in Poe- 

 cilia, as Duvernoy has pointed out, they are more less movable. In cer- 

 tain aspects the affinities of the genera are rather more apparent in them 

 than in the teeth of the jaws. 



To some extent the teeth are convenient for purposes of classification, 



