472 University of California Publications in Geology [Vol. 7 



Although the divergencies are expressed in nearly every part 

 of the skeletal structure, they are, in most instances, small in 

 amount. 



With regard to the tooth formula, Coues states: "It is said 



3 3 



that the young Sea Otter has I — - like all other Mustelidae. 



o — o 



. . . . " 17 Unfortunately, he omits the authority for this asser- 

 tion. If the young Latax does possess three incisors below on 

 each side, the different incisor formula of the genus would be 

 clearly shown to be not in any way a profound or fundamental 

 distinction. It may be questioned further whether the loss by 

 the sea-otter of P 1 is a difference any more deep-seated than the 

 loss of the middle pair of lower incisors. The loss of certain 

 anterior premolars is well known to be comparatively frequent 

 in fissipedian carnivores, while incisor loss is comparatively rare. 



The modification of the digits of the hind foot, though strik- 

 ing, would not seem to the writer to be of sufficient importance 

 to warrant the reference of the sea-otter to a subfamily distinct 

 from the Lutrinae. 



If La tax is left in the subfamily Lutrinae, the classification 

 in a measure fails to show the differences existing between the 

 two genera. If, on the other hand, the sea-otter is referred to a 

 distinct subfamily, the classification certainly does not indicate 

 the fundamental resemblances of the two genera. Apparently the 

 question is one of whether the differences or the resemblances 

 seem to the individual author of most significance. Baird, 18 Os- 

 born, 19 Trouessart, 20 Elliot,- 1 and Stephens 22 refer the sea-otter 

 to the subfamily Lutrinae, while Gill 23 and Coues 24 make it the 

 sole genus in the subfamily Enhydrinae. 



17 Coues, E., op. cit., p. 326. 

 is Baird, S. F., op. cit., p. 189. 



is Osborn, H. F., The age of mammals (i^iew York, the Macmillan Co., 

 1910), p. 531. 



20 Trouessart, E. L., Catalogus mammalium (Berolini, E. Friedlander 

 & Sohn, 1898, 1899), vol. 1, p. 281. 



21 Elliot, D. G., "Synopsis of the mammals of North America," Pub. 

 Field Columb. Mus., Zool. Ser., vol. 2 (1901), p. 351; and "Check list of 

 North American mammals," same series, vol. 6 (1905), p. 433. 



22 Stephens, F., California mammals (San Diego, West Coast Pub. Co. 

 1906), p. 232. 



=3 Gill, T., op. cit., p. 65. 

 24 Coues, E., op. cit., p. 325. 



