SLOTHS, ANT-EATERS, AND ARMADILLOS. 181 



as in the black-fish, the bony union between the two branches of the lower 

 jaw is short. The sides of the body are always marked by two light- coloured 

 areas, between which is a band, or a series of streaks of black. 



The second group of the family includes the true dolphins and their allies, 

 in all of which there is a distinctly defined beak, generally exceeding the 

 brain-cavity in length, and marked off from the hinder portion of the head by 

 a V-shaped groove. By sailors dolphins are indifferently spoken of either as 

 porpoises or bottle-noses, which frequently leads to a confusion between them 

 and either true porpoises or the bottle-nosed whales. They are divided into 

 numerous genera, according to the number of the teeth, the relative length 

 of the beak, and the conformation of the bones of the palate. They are all 

 comparatively small animals, but few exceeding a length of about 10 ft.; 

 and while most of them are marine, some ascend the larger rivers temporarily, 

 and others are permanent inhabitants of fresh- waters. Fish of various kinds 

 constitute the usual prey of dolphins, but it is believed that one species of 

 the genus Sotalia from the Cameruns district subsists on sea-weed. In the 

 true dolphins (Delphinus), of which there are several species, the beak is of 

 considerable length ; the flippers and back-fin are long and slightly hooked ; 

 there are from about forty to sixty-five pairs of sharp teeth in each jaw, 

 which have an oval section at the base; and the union between the two 

 branches of the lower jaw is short. In the bottle-nosed dolphins (Tursiops) 

 the beak is shorter and more tapering, and the number of teeth less, there 

 being generally from twenty-two to twenty-six pairs. A third genus is 

 typified by the rough-toothed dolphin (Steno frontatas), from the Atlantic 

 and Indian Oceans. Here the beak is greatly elongated, and the bony union 

 between the two branches of the lower jaw very long ; the rather large teeth 

 varying from twenty to twenty-five pairs, and being often marked by rough 

 groovings. Nearly allied are the long-beaked river-dolphins forming the 

 genus Sotalia, which may be distinguished by their fluviatile or estuarine 

 habits, and the smaller number of vertebrae in the backbone : the teeth being 

 always smooth, and the base of the flippers very wide. Several of the 

 species inhabit the Amazon-system, while one is found in some of the Chinese 

 rivers, and another in the estuaries and rivers of the Cameruns district. 



ORDER IX. EDENTATA. 



SLOTHS, ANT-EATERS, AND ARMADILLOS. 



THE three families of mammals named above, all of which are practically 

 confined to South and Central America, although one or two wander as far 

 north as Texas, are the representatives of an order in which all the existing 

 forms are devoid of front teeth, while the cheek-teeth have no external 

 coating of enamel, but consist solely of ivory, or of ivory with a layer of 

 cement. In consequence of this poor development of the teeth, the group is 

 known by the name of Edentata. To the same group have been commonly 

 referred the pangolins of the warmer parts of the Old World and the aard- 

 varks of Africa, but it is nearly certain that these cannot rightly be included 

 in the same order, and they are accordingly referred here to a group by 

 themselves. It is rather difficult to give many other characters in addition 



