CHARACTERS OF SUBGENUS LUTREOLA. 159 



addition to the comparative flatness of the auditory bulhe, some 

 constriction and outward prolongation of the meatus, which is 

 not seen in Gale or Cynomyonax^ and scarcelj^ indicated in Fu- 

 torius proper. The frontal outline is nearly straight, and but 

 little sloping (much as in Lutra). The pterygoids develop 

 strong hamular processes, also seen in Putorius proper, but 

 which are weak or wanting in Gale. There is much constric- 

 tion of the skull near the middle, and the postorbital processes 

 are well developed. 



The dentelure of Liitreola is probably the strongest to be 

 found in the genus Putorius at large, and there is reason to sup- 

 pose that it reaches a maximum in the large North American 

 species of this subgenus. In L. vison,* the teeth, aside from the 

 lesser number of premolars, are singularly like those of Mustela 

 martes, as a matter of superficial resemblance j and the supe- 

 riority in size and strength over those of Putorius proper, or of 

 Cynomyonax (not to mention Gale), is very evident on compari- 

 son. In the American, if not in other species of Lutreola, the 

 following points may be specially noted : — 



The back upper molar is of relatively large size, conspicu- 

 ously exceeding that of Putorius fcetidus or Cynomyonax nigripes 

 in relative as well as absolute bulk. The inner moiety is much 

 larger than the outer ;f its free border is nearly circular; it is 

 divided from the outer by a strong constriction ; the outer is 

 somewhat trefoil-shaped. The inner moiety presents a raised 

 rim and a central tubercle ; the outer has a corresponding 

 tubercle, but the border is divided into two prominences, mak- 

 ing three in all on this half of the tooth. The posterior upper 

 premolar (sectorial tooth) shows certain characters not shared by 

 any American species of the genus at large. There is devel- 

 oped, at the ^ntG)VO- external corner of the tooth, a decided pro- 

 cess or spur, only less in size than the ordinary ^nt^vo -internal 

 one ; and the projection of this gives to the outer border of the 

 tooth a decidedly concave outline.}: This process, together with 

 the internal one, gives the fore end of the tooth a V-like re- 



^I have not been able to examine the teeth of any Old World species of 

 this subgenus. 



t This is not the case either with P. faiidus or C. nUjr'ipes, but is scarcely a 

 subgeueric character, for it is said not to occur in the European species of 

 Lutreola. 



t There is a trace of this process in P.fwtidus and C. nigripes, but it is not 

 sufficiently developed to render the outer border of the tooth concave, nor 

 to make a V-ret'ntrance at the fore end. 



