122 



ANATOMY OF THE WOOD RAT 



be an insignificant subgeneric variation or not. The maxil- 

 lary tooth rows are more nearly parallel in Teonoma than 

 in the other two, but to too slight an extent to constitute a 

 good subgeneric criterion. The molars are a shade the 

 broadest in Homodontomys, and narrowest in Teonoma. 

 The third upper molar is slightly smaller in Neotoma than in 

 the other two, and this is stressed by Goldman (1910) as a 

 good character by which Homodontomys may be separated 

 from Neotoma; but I consider this difference also too slight 

 to be of much subgeneric importance. 



Each molariform tooth row consists of three teeth. The 



Fig. 26. Enamel pattern of right upper series of molariform teeth of 

 A, Homodontomys, B, Teonoma, and C, Neotoma, selected to show the same 

 stage of wear of the third tooth. 



first or anteriormost of the upper molars has three enamel 

 spaces, formed by two outer and an inner reentrant angle. 

 In addition, the antero-internal enamel face may or may not 

 be indented to a variable degree. The second molar, al- 

 though of somewhat different configuration from the first, 

 also has three enamel spaces, two outer and an inner re- 

 entrant angle. The same description appHes to the third 

 molar as well, although this again differs in shape from, and 

 is smaller than, the other two. In Homodontomys, a second- 

 ary reentrant angle of the postero-external angle often ex- 

 hibits a tendency to bisect the middle enamel space. This 



