•176 University of California Publications in Geology [Vol.7 



this classification of the characters is subject to modification, and 

 the statistical statement not all that could be desired, since 

 account cannot well be taken of the relative importance of the 

 characters, still it is believed that in the main what seems to be 

 shown is verv near the truth. 



OSTEOLOGY AND DENTITION OF LATAX 

 Skull 



The comparative size of three skulls examined is shown by 

 the following measurements, all in millimeters: 



Lutra canadensis Latax lutris Latax lutris 



nereis (no. 6956) lutris (no. 8124) 



Greatest length of skull — most 

 posterior surface occipital con- 

 dyle to most anterior surface 



of premaxillary 106.8 114.1 132.9 



Height of skull at auditory 

 bulla — taken perpendicularly 



to basieranial axis of skull 36.9 60.2 63.7 



Greatest breadth of skull at 

 mastoid process, measured ex- 

 teriorly 63.2 83.1 97.7 



These dimensions indicate the heavy and massive character 

 of the cranium of the sea-otter, and clearly show that as com- 

 pared with the skull of Lutra canadensis that of Latax lutris 

 nereis is larger relatively to length of trunk. 



The brain-case is more bulky in the southern sea-otter (no. 

 6956) than it is in the river otter, th.e skull of Latax I. lutris (no. 

 8124) having this bulkiness still more emphasized. 



The latter skull (no. 8121) evidently belonged to an old 

 animal (possibly a male), as the sutures are discernible in only a 

 few places, and the sagittal crest and lambdoidal ridge, as well 

 as other processes for muscle attachment, are very highly devel- 

 oped. 



The lateral boundary of the anterior nares, formed by the 

 premaxillaries, is in the sea-otter more nearly perpendicular than 

 in the river otter. Consequently, the skull may be described as 

 being high anteriorly, the nasals being more above the incisors. 



