354 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



time farther than it does in the remaining genera. The internal 

 third of the reentrant angle is rather wide, as it is in Pronolagns. 



In the remaining genera, Lcpns, Oryctolagus, Sylvilagus, and 

 Liiunolagus, the reentrant angle of the second, third, fourth, and 

 fifth upper molariform teeth is crenated and extends about three- 

 quarters of the distance across the tooth. In Liiunolagus the in- 

 ternal fourth of the fold is rather wide, resembling the condition 

 seen in Romcrolagus and in Pronolagns. In Lepns, Oryctolagns, 

 and Sxh'ilagns the sides of the reentrant angles are almost in contact 

 wath one another throughout their whole extent. 



In the second, third, and fourth lower molariform teeth of Brachy- 

 lagus the single external reentrant angle divides the tooth into the 

 usual anterior and posterior portions, but the latter portion has only 

 about half the side-to-side diameter that the anterior portion has. 



In Pronolagns, Ronicrolagns. and Pcntalagus the posterior por- 

 tions of the second, third, and fourth lower molariform teeth have 

 lateral diameters ecjualing those of the anterior portions, but in 

 Pcntalagus the fold of enamel dividing these teeth into anterior and 

 posterior portions is very deeply convoluted, very much more than 

 it is in any other genus of the Leporidae. 



In Lcpus, Oryctolagus, Syhilagns, Liiunolagus, and Caprolagns 

 the lateral diameters of the posterior portions of the second, third, 

 and fourth lower molariform teeth are about four-fifths the lateral 

 diameters of the anterior portions. 



In all the genera the third upper molar is much reduced in size 

 and is elliptic in section, and in Pcntalagus it is not found at all. 

 It is larger in Pronolagns, however, and is somewhat diamond- 

 shaped. In Caprolagus it is relatively much smaller than it is in 

 the rest of the Leporidse. 



The last lower molar has the appearance of a double cylinder in 

 all the genera, the anterior portion of which is larger and more 

 elliptical in section, the posterior portion smaller and more terete. 

 In Pronolagns, the reentrant angle, which divides this tooth into 

 the two mentioned portions, is more marked than it is in the other 

 genera, and the posterior face of the anterior cylinder is slightly 

 indented. 



OCHOTONID.E 



( Plate XCI, i ) 



The dental formula of the Ochotonidae is I |, C ^, Pm. |, M 



|, being the same as that of the Leporidae with the exception 



of the small last upper molar, which has been so reduced in Ochotona 



as to have disappeared, as is also the case with Pcntalagus of the 



