lvon] the hares and their allies 387 



h'} Sutures of the interparietal distinct throughout life. 

 k) Choanje narrow. Genus Orycfolagus, p. 402. 

 k') Choanas not narrowed. Genus Sylvilagns, p. 396. 

 g') First lower premolar with two crenated reentrant angles on 

 its anterior face. 

 /) Internal face of anterior portion of first lower premolar 



without reentrant angle. Genus Limnolagiis, p. 406. 

 /') Internal face of anterior portion of first lower premolar 

 with reentrant angle. Genus Caprolagus, p. 426. 



B. Key to the Families, Genera, and Subgenera of Existing Hares, 

 Rabbits, and Pikas, Based on Cranial Characters 



a) Postorbital process absent, skull flat, much constricted between orbits, 

 rostrum short and slender, nasals widest in front, bony palate very short, 

 posterior free edge of malar very long, maxilla not conspicuously fenes- 

 trated, mental foramen of mandible situated under last lower molar. 

 Family Ochotonid.e, genus Ochotona, p. 431. 

 b) Interorbital region very narrow and pinched up and stronglv arched 



from before backward. Subgenus Ochotona, p. 438. 

 b') Interorbital region moderately broad, not compressed laterally nor 

 arched from before backward, 

 c) Brain case and whole skull very flat, rostrum slender, its origin 

 abrupt, no foramen in the anterior part of the frontal bone. 

 Opening in maxilla single, roundly triangular. Incisive 

 foramina constricted into two unequal portions. Subgenus 

 Pika, p. 438. 

 c') Brain case rather rounded, whole skull moderately arched from 

 before backward, rostrum relatively long and heavy, its origin 

 not abrupt, a small oval foramen in frontal bone. Opening in 

 maxilla elongated triangular with a small amount of fenestra- 

 tion just beneath it. Incisive foramina triangular in outline, 

 not constricted into two unequal portions. Subgenus Conothoa, 

 P- 438. 

 a) Postorbital process well developed, skull arched from before backward, 

 moderately constricted between the orbits, bony palate only moderately 

 short, rostrum long and stout, nasals widest behind, posterior free edge 

 of malar only moderately long, sides of maxilla more or less con- 

 spicuously fenestrated, mental foramen of mandible situated under first 

 lower cheek tooth. Family Leporid.b. 

 d) Postorbital process attached to the side of the skull for its whole 



length. Genus Liinnolagiis, p. 406. 

 d') Postorbital process not attached to the side of the skull for its whole 

 length, bounding well marked foramina or notches. 

 e) Postorbital process small, without anterior limb, the single pos- 

 terior limb pointed, directed outward and backward, bounding 

 a distinct notch. Bony palate long. 

 f) Nasals relatively short, as broad in front as behind. 



•g) Incisive foramina elongated triangle in outline, postorbital 

 process smaller and pointed. Genus Caprolagus, p. 426. 



