CHARACTERS OF SOME SPECIES OF LUTRINiE. 545 



Skunks, the palatine foi'amina in question placed on the maxillo- 

 palatine suture. 



Both Mustela a.nd Grison are predatory terrestrial forms ; and 

 on a priori grounds it seems to be much more probable that the 

 Otters are the descendants, modified for aquatic life, of some 

 group of active, predatory terrestrial Mustelidfe than of com- 

 paratively inactive, specialized diggers like the Badgers. This 

 view is supported by the long, slender, flexible body, the long 

 tail, the broadly webbed, well spread digits, small claws and small 

 front paws. These charactei'S are found associated only in the 

 genera currently referred to the Mustelinae, but not in any of 

 the so-called Melinse, which have a short thick body, short tail, 

 closely tied toes, powerful claws, especially on the fore feet, and 

 the latter are larger than the hind feet. 



Another point worth considering is the presence in a few 

 unrelated species — i.e. Lutra canadensis, according to Gray, and in 

 Hydrictis maculicollis and Amblonyx cinerea — of hairs upon the 

 lower side of the webs of the feet. It seems to me to be difficult 

 to explain their occurrence on the hypothesis of the descent of 

 the Otters from naked footed Meline burrowers. The hairs seem 

 to be quite functionless, and they have all the appearance of 

 harmless vestigial structures suggesting the descent of Otters 

 from hairy-footed forms. And since the Martens, Wolverenes, 

 and Weasels, in the broad sense of the word, are the only members 

 of the Mustelidse, apart from the Otters just mentioned, which 

 have hair upon the webs below, these hairs may be regarded as 

 an additional item of evidence pointing to those active predatory 

 Mustelidse as standing nearest to the extinct ancestors of the 

 Otters. 



It is not of course suggested that the Otters are the descendants 

 of any of the Martens or Weasels known to \\s, but that they are 

 an offshoot from that line of descent; and I visualize their ancestor 

 as an active terrestrial, predatory Mustelid with a well-developed 

 tail and feet with the longish digits provided with short, sharp 

 claws and united by wide webs, hairy below but not so hairy as 

 in Martes or Mustela, and with the pads probably as large as in 

 Charronia, with the skull shaped like that of Mustela or Grison, 

 the auditory bulla like that of Martes and also the dentition, 

 except that the upper carnassial had a larger inner lobe such as 

 is seen in Grison. 



The enlargement of the hind feet as compared with the fore 

 feet, the thickening of the facial vibrissse, with the correlated 

 expansion of the upper lip and enlargement of the suborbital 

 foramen, the reduction and simplification of the ear, the texture 

 of the fur, and the muscular development of the tail, are special 

 adaptions to aquatic life. Similarly, the enlargement of the back 

 teeth, recalling in a measure that of the Melinge, may be looked 

 upon as an adaptation for breaking up fish-bones and rendering 

 them harmless to swnlloAv. 



The explanation of the great difference in dentition between 



37* 



