3 50 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



which angle are more or less crenated. The enamel is well marked 

 in this loop and on the anterior and posterior faces of the teeth, 

 but it is scarcely discernible on the outer sides. 



The last upper molariform tooth is very small, subterete, and with- 

 out reentrant angles. 



The lower molariform teeth, while built essentially on the same 

 plan as the upper molariform teeth, are more difficult to understand, 

 owing to the greater extent of the infolding of enamel which takes 

 place in all the teeth, even the last small tooth. The infolding of 

 the enamel is on the outer side of these teeth, and not the inner side, 

 as in the case of the upper molariform teeth. 



The first lower molariform tooth is divided into an anterior and 

 a posterior portion in most Leporidce by a single deep reentrant angle 

 extending across the tooth from the external face. In three genera, 

 however, Romerolagus, Fronolagns, and Pentalagus (and perhaps 

 A'esolagiis), this tooth is divided into anterior and posterior portions 

 by two reentrant angles, each extending half-way across the tooth, 

 one from the external face and one from the internal. The anterior 

 portion of this tooth has various minor reentrant angles on the 

 anterior or lateral surfaces, or on both. Each of the second, third, 

 and fourth lower molariform teeth appears like a double tooth of 

 two compressed parts, of which the more anterior is the larger and 

 stands higher up. 



The last lower molariform tooth is much reduced in size, but 

 similar to the others in structure, with a larger elliptic anterior por- 

 tion and a smaller rotund posterior portion. 



Following are the tooth variations in different genera of the 

 Leporidse : 



Incisors. — The groove on the anterior surface of the first 

 upper incisor is shallow and is not filled with cement in Pocci- 

 lolagiis, Oryctolagns, Brachylagns, Pentalagus, nearly all the mem- 

 bers of Sylvilagiis (where, however, the groove is deep and in 

 some Mexican specimens it is filled with cement), Ronicrolagus 

 (where the groove is still deeper), and Pronolagus. Lcpus 

 {Macrotolagns) calif ornicus has a shallow unfilled groove. Most 

 members of the subgenus Lcpus have deep grooves, usually without 

 cement. 



The groove is shallow and filled with cement in Linniolagns and in 

 Leptis tibctanus. 



The groove is rather deep but simple and filled with cement in 

 Lcpus {Lcpus) cauipcstris, in Lcpus yarkandcnsis, in Lcpus 

 ochropus, in Lcpus (Macrotolagns) tc.viaiins, and in Caprolagus. 



