52 University of California Publications in Geology [Vol. 13 



ranging on the eastern coast of South America as far north as 

 Uruguay, and as far east as Kerguelen Island and the Cape region 

 of Africa, The distribution of the otarids in the past corresponds 

 very well with this. The finding of a humerus of a marine mammal 

 in the Pleistocene brick clays of Dunbar, Scotland, which may pos- 

 sibly belong to some unknown otarid 44 may prove to be an exception 

 to this statement. The fact that the earlier Otariidae were not so well 

 adapted to aquatic life as were the Odobenidae, and therefore were 

 not capable of such wide dispersal may explain why they did not 

 migrate across this open sea of submerged Central America 45 during 

 the Oligocene or early Miocene time along with the Odobenidae. This 

 explanation hardly seems probable because Arctocephalus fischeri is 

 known, through the investigations of Ameghino, 46 from the lower 

 Miocene of Argentina, South America. The Odobenidae, as has 

 already been stated, are not known in Europe until the Lower Pliocene. 



The resemblance of the mandibular rami of Prorosrnarus and 

 Alachtherium to the type of rami exhibited by the Otariidae is 

 undoubtedly a common inheritance from more primitive ancestors. 

 The bones of the manus of Trichccodon and of Alachtherium as 

 figured by Van Beneden 47 show that there is a close resemblance 

 between the metacarpals possessed by these genera and similar bones 

 of the genus Eumetopias. Some of the differences, such as the curva- 

 ture of the horizontal ramus, the reduction of the molars, and change 

 in arrangement of the dental battery, are essentially due to subsequent 

 specialization, and other primitive characters, such as a very long and 

 unankylosed symphysis, the presence of the second and third lower 

 incisors together with a single canine which still retains its caniniform 

 shape, and the retention of the lower fourth premolar, point to a 

 closer relationship. On the other hand, the loss of the first and 

 second lower molars indicates a more remote divergence in the genea- 

 logical series, possibly during early Miocene or late Oligocene. At 

 any rate the period of divergence was at a much remoter period than 



Thompson, A. W., Jour. Anat. and Phys., vol. 13, pp. 318-321. 1879. 

 Turner, W., The marine mammals in the anatomical museum of the University 

 of Edinburgh, pt. 3, p. 186, text fig. on p. 187. London, 1912. 



45 Vaughn, W. T., The biologic character and geologic correlation of the sedi- 

 mentary formations of Panama in their relation to the geologic history of Central 

 America and the West Indies. Bull. 103, U. S. Nat. Mus., pp. 607-609. 1919. 



46 Ameghino, F., Contribueiones al conocimiento de los mamiferos fossiles de 

 los terrenos terciarios antiguous del Parana. Bol. Acad. Nac. Cieneias, Cordoba, 

 Argentina, vol. 9, p. 21-4. 1886. 



*" Van Beneden, P. J., op. cit. Atlas, vol. 1, pt. 1, pi. 2, fig. 6, and pi. 7, figs. 

 6, 6'. 



