544 Bulletin American Museum of Natural History [Vol. LXVI 



acromion thinner, the tuberosity of the spine less pronounced. In the 

 matter of proportionate narrowness, inunguis is intermediate between 

 senegalensis and manatus, but in other characters it can hardly be 

 distinguished from manatus. The geographical representatives of 

 manatus show no constant peculiarities of the scapulae. 



The humerus of the Congo Expedition manatee is distinctly thinner 

 than that of Florida manatees of the same length. The weight of the 

 Congo humeri is just half that of a typical pair of the same length from 

 Florida. In this respect the Congo manatee is very closely similar to 

 inunguis. . 



The relative proportions of the humerus are carried into the radius 

 and ulna. In both senegalensis and inunguis these two elements are 

 about one half the diameter of corresponding elements in manatus. 



The metacarpals of the three species differ markedly in length. 

 The fourth digit is the longest, and measurements were therefore made 

 on the metacarpal and phalanges of this finger of each specimen. This 

 metacarpal grows more rapidly or for a longer period than does the 

 radius, and in consequence the metacarpal is proportionately longer in 

 older specimens than in young, when, as here, the length of the radius is 

 used as the unit of comparison. In specimens of approximately equal 

 age, however, differences are marked. Thus in manatees of the approxi- 

 mate size of our Congo specimen the metacarpal is about 54 per cent of 

 the radial length in manatus, about 64 per cent of the radial length in 

 inunguis, while in the Congo specimen the metacarpal is 62 per cent as 

 long as the radius. 



In the matter of the length of the first carpal, senegalensis is not 

 intermediate between the Caribbean manatees and inunguis but falls 

 within the limits of variation of manatus. This first phalanx of the fourth 

 digit does not grow as rapidly or over as long a period as its metacarpal, 

 with the result that with increased age it is in proportion to this meta- 

 carpal increasingly shorter, whereas its growth rate outstrips that of the 

 humerus, and increased age brings a proportionately, as well as an 

 actually increased length. 



Again comparing immature animals about the size of the Congo 

 specimen, it is found that the first phalanx in both manatus and sene- 

 galensis is about 25 per cent of the humerus length, or 40 per cent of the 

 metacarpal length (the specimens suggested that this element in the 

 Florida manatees is considerably longer than that in the Puerto Rican) , 

 whereas in inunguis the corresponding percentages are 40 and 60. 



The remaining phalanges follow the trend indicated by the first, 



