BONY FISHES AND GANOIDS. 501 



hippopotami, giraffes, rhinoceroses, elephants, and antelopes. From the 

 Cyprinidce the present family is broadly distinguished by certain peculiarities 

 in the structure of the skull, and by the number of upper pharyngeal bones being 

 one or four, in place of two. The margin of the upper jaw is also different, in 

 that it is formed in front by the premaxillae, and by the maxilte at the sides, 

 instead of entirely by the former bones. Barbels, too, are wanting ; but 

 whereas the head is as devoid of scales as in the CypriiMce., the jaws may be 

 either smooth or furnished with powerful teeth. In such an extensive family, 

 it is but little use referring to genera by name, when their distinctive 

 ' features cannot be described. It may be mentioned, however, that the 

 African and the American genera are distinct from one another, and that the 

 typical Erythrinus is from America. Two genera — of which Hydrocyon is 

 African, and Cynodon Tropical America — are, however, noteworthy on account 

 of the large size and predaceous habits of some of their representatives. 

 Two species of the former genus are abundant in the Nile, where they grow 

 to about four feet in length, and are respectively known by the Egyptians by 

 the names of Kelb-el-bahr and Kelb-el-moyeh. 



Section D. — Haplopomi. 



In this fourth section of the Physostomi the first four vertebrie of the 

 backbone are distinct from one another, and unmodified ; the supraoccipital 

 bone of the skull extends forwards to separate the two 

 parietals, and the full number of bones is developed in the Family 



gill-covers, or operculum. The pharyngeal bones, too, are Cyprinodoniidai. 

 separate, and in the upper jaw are three or four in number, 

 and directed forwards. The first family of the section is that of the 

 Cypriiiodontidm, which includes a considerable number of genera of small 

 fishes ranging over America, Africa, Asia, and the south of Europe, and 

 inhabiting alike salt, brackish, and fresh water. With a mouth devoid of 

 barbels, these fish are easily recognised by the scales extending on to the 

 head, as well as by the absence of a fatty dorsal fin, and the backward 

 position of the rayed dorsal. As in the carps, the margin of the upper jaw is 

 formed entirely by the premaxillary bones. Tlie third upper pharyngeal 

 bone is enlarged, and teeth are present, not only on the pharyngeals, but 

 likewise in the margins of the jaws. Whereas some cyprinodonts feed on 

 living animals, others seek their food in mud. The males, which are much 

 inferior in size to their partners, include some of the smallest of aU living 

 fishes ; and most species produce their young in a living condition. In a 

 family so extensive, it is difficult to select genera for special mention. The 

 typical Cyprinodon has a very wide distribution, and is represented by seven 

 species from the countries bordering the Mediterranean. Some of its 

 members are remarkable for inhabiting springs or pools almost saturated with 

 salt, while others are found in springs of very high temperature. Perhaps 

 the most noteworthy forms are the species of the genus Anableps from 

 Tropical America, in which the eyes are divided by a horizontal line into an 

 upper and a lower half. The convexity of the lens differs in these tvro halves, 

 the upper half being suited to vision in air, and the lower in water. This 

 enables the fish to see perfectly in both media when swimming near the 

 surface of the water, with one half of the eye below, and the other above, the 

 surface. A good account of the habits of these curious fishes has been 



