SKULL AND TEETH OF ENHYDRIS LUTRIS. 333 



the jaw. I have not witnessed such case. The back wall, in- 

 stead of overlapping strongly at its outer angle, is regularly 

 produced into a border all along. The inflation of the bullsB is 

 about as in Lutra, The posterior foramen lacerum is a large 

 circular hole. The articular surfaces of the condyles differ from 

 those oi Lutra in not being produced toward each other; they 

 are simply oval. The great foramen is irregularly circular 

 rather than transversely elliptical, having a strong median supe- 

 rior as well as inferior emargination. In the under jaw, the 

 symphysis is shorter and apparently less solid than usual. I 

 find the union incomplete in some middle-aged specimens. The 

 ramus of the under jaw is deep and thick, and has a decided 

 twist, scarcely or not recognizable in other genera, by which the 

 lower part is exflected posteriorly. The coronoid is very broad 

 to the rounded end j the hind border rises straight and a little 

 obliquely backward, so as to overhang the condyle; the front 

 border is strongly, somewhat irregularly, curved. The muscu- 

 lar impression on the outside of the coronoid is deep and exten- 

 sive, reaching below to the very edge of the jaw, and forward 

 to a point below the last molar. 



The dentition of JEnhydris is peculiar in several respects. As 

 in Liitrince, but not as in any other subfamily of Mustelidce, there 

 is the same number of teeth in both jaws (16) ; but this equality 

 is brought about in a curious way, loss of the upper anterior 

 premolar being rectified, so far as preserving equality of teeth 

 in the two jaws is concerned, by lack of one pair of inferior 

 incisors. Thus there are four fewer teeth than in Liitrinw (i| 

 instead of {f ). This is the only instance in the family of less 

 than six incisors below, or of an unequal number of incisors in 

 the two jaws. In the presence of an equal number of premolars 

 above and helow, Uiihydris agrees with all the other North Amer- 

 ican genera excepting Xw^m (^) and normal Conepatus (^[|); in 

 the presence of three premolars above and below, it agrees with 

 all but Lutra, Conepatus, Mustela, and Gulo (the two last having 

 ^); in the presence of three premolars below, it agrees with all 

 excepting Mustela and Gulo. 



In the physical character of the teeth, as well as in the dental 

 formula, Enhydru is peculiar in its family. All the grinders are 

 of a singularly massive, tubercular, almost bulbous character, 

 with no trenchant edges, acute cusps, or even angular edges. 

 This is in evident adaptation to the piscivorous regimenjof the 

 animal. The teeth of even the youngest specimens^^have an 



