3^^ SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



VI. KEYS TO FAMILIES, GENERA, AND SUBGENERA OF THE 



DUPLICIDENTATA, BASED ON DENTAL, CRANIAL, 



AND OTHER SKELETAL CHARACTERS 



A. Key to the Families and Genera of Existing Hares, Rabbits, and 

 PiKAS, Based Mainly on Dental Characters 



a) Dental formula: If, C ^, Pm |, M f, second upper molariform tooth 

 unlike third in form. Family Ochotonid^e, genus Ochotona, p. 431. 



a) Dental formula usually I f , C §, Pm f, M | (in Pentalagits the molars are 

 f), second upper maxillary tooth like third in form. Family, Lepo- 

 RID.«, p. 389. 

 b) Reentrant angle of second upper maxillary tooth short and not crenated. 



c) Reentrant angle extends one-third way across the tooth, genus 



Nesolagiis. p. 425. 

 c') Reentrant angle extends half way across the maxillary teeth, genus 

 Brachylagus, p. 411. 

 b') Reentrant angles of second, third, fourth, and fifth maxillary teeth 

 with sides crenated. 



d) First lower premolar divided into an anterior and a posterior 



portion by two reentrant angles, one extending from the ex- 

 ternal, the other from the internal face to the center of the tooth. 

 e) Anterior face of first lower premolar without reentrant angles. 



Genus Romcrolagits, p. 420. 

 e') Anterior face of first lower premolar with two reentrant 

 angles. 

 f) Posterior limb of reentrant angles of second, third, and 

 fourth mandibular cheek teeth with antero-posterior 

 convolutions nearly as long as the antero-posterior 

 diameter of the posterior portions of the teeth. Genus 

 Pcntalagns, p. 428. 

 /') Posterior limb of reentrant angles of second, third, and 

 fourth mandibular cheek teeth w-ith normal convolu- 

 tions, not nearly so long as the antero-posterior 

 diameter of the posterior portions of the teeth. Genus 

 Prouolagus, p. 416. 

 d') First lower premolar divided into an anterior and posterior por- 

 tion by a single deep reentrant angle extending entirely across 

 the tooth from its external surface, 

 g) First lower premolar with but one reentrant angle on its 

 anterior face. (Some Alexican Sylvilagiis have two.) 

 /;) Sutures of the interparietal obliterated in the adult, genus 

 Lcpus, p. 389. 

 Groove on incisors not filled with cement. Subgenus 

 Pcccilolagus, p. 395. Also some Lcpus and Macro to- 

 lagiis. 

 i') Groove on incisors filled with cement. 



/) Groove deep and simple. Mostly subgenus Lcpus, 



p. 394- 

 ;') Groove deep and bi- or tri-furcated. Mostly sub- 

 genus Macrotolagus, p. 395. 



