1934] Hatt, African Manatees 549 



different pattern in the three species. In senegalensis the orbital process 

 of the frontal diverges most strongly in a lateral direction, and the upper 

 orbital borders formed by this process are strongly convergent in the 

 African and Amazonian manatees. This latter character is a configura- 

 tion well marked even in the newborn. If the line of the outer border of 

 this orbital process is extended forward, it will cross the median line 

 anterior to the end of the skull in manatus, whereas in senegalensis and 

 inunguis this crossing occurs within the limits of the skull. 



The age of the individual manatee determines the degree of back- 

 ward divergence of the postorbital process of the orbital process of the 

 frontal, and at the same time the closure of the orbital ring. In all 

 species this occurs only late in life and is seen in few specimens, though 

 it would appear that this closure is more frequent and occurs earlier in 

 life among Guatemalan than among Florida manatees. 



The infraorbital foramen in manatees is ordinarily simple, though it 

 may be divided in manatus. Hartlaub observed that in this species 

 the division was frequent, but, with the exception of two of four Guate- 

 malan skulls examined, I have not found such division in any specimen 

 of manatus. As most of my manatus skulls are from the northern limits 

 of the species, and those of Hartlaub from the southern limits, it is 

 possible that a divided infraorbital foramen is of more frequent occur- 

 rence in the south than in the north. 



The bony ridges formed at the superior border of the temporal 

 muscle are more or less vertically directed in senegalensis and manatus, 

 while in inunguis these ridges are produced laterally and do not rise 

 above the general level of the skull roof. 



The malar process of the temporal in manatees is swollen and spongy 

 in nature. At the anterior end the thin layer of compact bone sheathing 

 the spongy mass is frequently discontinuous, and a rough or perforated 

 surface is common. However, when the surface is reasonably uninter- 

 rupted, it is smooth in senegalensis and always rugose in inunguis. This 

 same area in manatus from Florida is fairly well-grooved in most speci- 

 mens, though this condition does not appear to apply to the species as a 

 whole, the same area in a manatee from Puerto Rico, one from Texas (?), 

 and three from Guatemala being smooth. 



The zygomatic process at its base is much thicker in senegalensis and 

 manatus than in inunguis. 



The malar bone sends a process downward which, in senegalensis, is 

 broad and sharply truncated. Specimens of manatus closely approach 

 this shape in some instances, but often have a backwardly directed 



