228 PROCEKDINGS OF THE ACADEMY OF [1894. 



ing forward more than half way from squamosal root to maxillary 

 plate; sagittal area subquadrate, usually broader than long; angular 

 process of mandible narrow, everted, lianiular, and thickened at end; 

 infracondylar notch low and deep. 



Subfamily NEOTOMIN^. 



Cranium not abruptly constricted in front of brain case, which is 

 oval, gradually narrowing into orbit ; orbital and temporal fossie 

 indistinguishable, without trace of separation ; jugal wholly poste- 

 rior, forming insignificant part of zygoma and never reaching for- 

 ward half-Avay from squamosal root to maxillary plate ; sagittal 

 area elongated, at least twice as long as broad ; angular process of 

 mandible broadly expanded vertically, inflected, not hamular, and 

 never thickened at end ; infra-condylar notch high and shallow. 



The dental characters of the Neotomiuic may be defined as fol- 

 lows: Molars !p prismatic, rooted or semi- rooted; the crowns fiat, 

 their sides continuously invested with enamel which is folded on 

 itself in such manner as to present on each side of the tooth a series 

 of salient loops, alternating with re-entrant angles or interspaces 

 (figs. 1-5). M ', -, and ^, each with three salient loops and two 

 re-entrant angles on outer side ; m ^ with three salient loops and 

 two re-entrant angles on inner side ;' m ^ and ^ each with two salient 

 loops and one re-entrant angle on inner side ; m ^ with three salient 

 loops and two re-entrant angles on outer side and four salient loops 

 and three re-entrant angles on inner side , with or without an ante- 

 rior lobe; m •_> (normally) with three salient and two re-entrant 

 angles on each side {^Ptyssophorus resembles Sir/modoii in having 

 the antero-external re-entrant angle small] ; m y variable, but 

 normally with two salient and one re-entrant angles on each side. 



The subfamily Neotominfe comprises the genera Neotonia, Xenoniys, 

 Hodoviys, TreUunys, and Ptyssophorm (and probably one or two 

 others). 



The Neotomina' may be distinguished from the Sigmodont ('rice- 

 tines by the following characters: — 



Molar crowns prismatic ; loops distant ; enamel folds of equal 

 thickness; crowns flat; antorbital vacuities without spine; palate 

 excavated between posterior molars Subfamily Neotominse. 



' In Neotonia desertonini and arizonce the antero-intenuil lodp is short and 

 shallow and becomes obsolete with wear (fig. 5a). 



