1910.] 



VARIATION OF THE SEA-ELErHANTS. 



581 



percentages of the basal length of the skull may be reckoned, as 

 is done below. 



Falkland. Macquarie. 

 " Basal length " 20 ins. 18 ins. 



(= 500 mm.) (= 450 mm.) 

 Maximum width in percent. 



of basal length 75 77"7 



Length of palate in ditto 55 52*7 



Width of palate in ditto 36 - 5 35 



Some of these relations thus appear at first sight to be 

 rather different in the different animals, but before any decision 

 can be made it is of importance to find out how constant these 

 percentages are when a somewhat greater number of skulls are 

 measured and compared. To obtain knowledge about this 1 have 

 measured seven skulls of adult and serniadult bulls of Sea- 

 Elephants, all of them from South Georgia. The largest of these 

 is 3 cm. longer than Lydekker's largest skull, and the smallest 

 0"7 cm. shorter than his smallest skull. The material might thus 

 be regarded as comparable. The relative dimensions of the South 

 Georgia skulls are recorded in the accompanying table of 

 measurements. From this it is apparent that the zygomatic 



width — as usual among large mammals — is subject to considerable 

 variation, viz. from 68*3 to 79'8 per cent, of the basal length of 

 the skull, but usually it is about 72-75 per cent. A comparison 

 reveals, then, that with regard to this dimension three of Lydekker's 

 specimens, representing "M. I. falclandicus " and " M. I. macquari- 

 ensis," fall within the limits of variation for the Sea-Elephant of 



