540 Bulletin American Museum of Natural History [Vol. LXVI 



Individual Variation and Asymmetry 

 The range of variation in manatees is so extensive that Gray de- 

 spaired of finding stable characters on which species nomenclature could 

 be founded. Better series of specimens than were available to Gray, 

 however, allow some sorting out of the characters, and it is an easy 

 matter to distinguish at least three species of manatees, no matter how 

 extensive their peculiarities, though occasional specimens are encountered 

 that vary, not only in the form and proportion of a few characters, but 

 very markedly in almost every character. Lacking a good series for 

 comparison, these variants would appear to represent well-marked 

 " species." Thus I examined the skeleton of one medium-sized Florida 

 manatee in which the bones are lighter, more compact, and more strongly 

 ridged than in any other specimen. 



Asymmetry is uncommon and where present is pathological. On 

 one young Florida skull the left occipital condyle is very nearly double 

 the size of the right, but the bone forming it is rough and irregular. In 

 another Florida specimen the diameters of the humerus, radius, and ulna 

 of the left side are approximately 25 per cent greater than those of the 

 other side, but here too the form of the bones is definitely anomalous. 

 The sternum of a third Florida specimen is greatly warped to one side. 

 The teeth of an adult Amazonian animal are completely disorientated, 

 some of the teeth of each row, even those unerupted, lying with the 

 direction of their ridges as much as 180° from the normal position. 



The External Anatomy 

 When the wide range of variability shown in the external form of the 

 species manatus, as documented by several accurate drawings, good 

 photographs, and casts, is considered, it is deemed that from external 

 characters senegalensis and manatus cannot be told apart. However, 

 the species inunguis is, in all likelihood, constantly characterized by the 

 absence of nails, a white breast patch, slender proportions, and elongated 

 flippers. 



The Vertebral Column 

 The Congo specimen possesses six cervical vertebrae, as do the 

 other members of the genus. The rib-bearing vertebrae vary in number 

 in Florida manatees (in a series of 11 skeletons) from 17 to 19; a Puerto 

 Rican specimen has 17 such vertebrae, and each of two Amazonian 

 manatees has 15 pairs of ribs. (Blainville's figure shows 16 pairs.) 

 The presence of 17 pairs in the Congo specimen (Buttikofer's specimen 



