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. Pseudobranchize 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 and broad. Belonesox 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 Haplochilinze to the com- 
pressed tricuspids of Cyprinodon, or to the broad oar-shaped movable ones 
of Poecilie. 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 
many 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, 
