1934] Halt, African Manatees 561 



A study of the skeletons of the species of manatees shows that the 

 principal postcranial differences lie in the proportion of the elements of 

 the pectoral girdle. T. senegalensis has lightly built bones and hands 

 proportionately about as long as those of manatus. The pectoral limb 

 bones of manatus are about double the diameter of those of the African 

 manatees, though their proportionate length is similar. The limb bones 

 of inunguis are lightly built like those of senegalensis, but the distal 

 elements, particularly the metacarpals and first phalanges, are consider- 

 ably more elongate than those of the other two species. 



The sterna of the three species are of distinctive types. These are 

 shown in figure 1. 



The differences in the skulls, for knowledge of which we are mainly 

 indebted to Hartlaub, are centered principally about the nasal basin. 

 Individual variation, which is so extensive in the genus, hinders the 

 formulation of invariable criteria for the distinction of the species, but 

 this variation is most pronounced in such vestigial parts as the lacrimal 

 and nasal bones. Perhaps the most constant specific character of the 

 skull is the length of the vomer. In senegalensis this usually extends 

 only to the level of the middle of the orbits, in inunguis to the anterior 

 edge of the orbits, and in manatus to the posterior edge of the incisive 

 foramen or beyond. 



Mandibular characters are well marked, though, in the main, subject 

 to considerable age variation. The species inunguis is easy to recognize, 

 among other features, by the large number of mental foramina (ten or 

 more), manatus by its deep symphysial groove, and senegalensis by its 

 lack of such a groove. 



The range of the African manatees extends along the West African 

 coast from Senegal to the Quanza River in Angola, and this full coastal 

 range is represented by scattered specimens in the museums of Europe. 

 The manatees are not known from far up any of the rivers flowing into 

 this coast, if we except the Niger and its tributaries. A specimen in the 

 British Museum was found along the Benue, and published reports 

 make it seem certain that manatees occur in the upper Niger River 

 above Timbuctu. It is also probable that manatees have occasionally 

 been taken in the Lake Chad drainage, into which they are supposed to 

 have gained access by crossing the seasonally flooded area lying between 

 the Benue and the Shari. Reports of manatees in the Uele, Lake Tana, 

 east of the Cape of Good Hope, and St. Helena are discredited. 



