384 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



[vol. 45 



PHALANGES 



Little can be said regarding the toes. The two lateral digits are 

 relatively longer in the Ochotonidse than they are in Leporidse. In 

 Oclwtona, Ronicrolagns, Pronolagns, Liiiuiolagiis, Oryctolagiis, and 

 Brachylagns the combined lengths of the three phalanges approxi- 

 mately equals the length of the metatarsal to which they belong. In 

 the other genera, Lcpus and Sylz'ilagiis, this is true of the middle 

 digits only ; in the case of the lateral digits the metatarsals are de- 

 cidedly longer than the combined length of the corresponding 

 phalanges. 



V. OSTEOLOGICAL DIFFERENCES BETWEEN 



AND LEPORID.E 



OCHOTONID^ 



The principal osteological differences between the two families 

 Ochotonidse and Leporidse, discussed in the foregoing pages, are 

 briefly set forth in the following table : 



OCHOTONID.E 



Leporid.e 



Skull 



Not arched, flat, much constricted 

 between the orbits. 



Rostrum short and slender. 

 Nasals widest in front. 



Palate very short. 

 Postorbital processes lacking. 



Posterior free edge of malar very 

 long. 



IMaxilla not conspicuously fenes- 

 trated. 



Mental foramen of mandible far 

 posterior to its usual position. 



More or less arched, not flat, only 

 moderately constricted between the 

 orbits. 



Rostrum long and stout. 



Nasals not wider in front than be- 

 hind. 



Palate moderately short. 



Postorbital processes well devel- 

 oped. 



Posterior free edge of malar only 

 moderately long. 



Maxilla more or less conspicuously 

 fenestrated. 



Mental foramen of mandible an- 

 terior, in its usual position. 



Teeth 



Dental formula 



I f C g Pm f M I 



Enamel not crenated in reentrant 

 angles of upper cheek teeth. 



Cutting edge of first upper incisor 

 V-shaped. 



Third upper molar entirely want- 

 ing. 



Second and fifth upper cheek teeth 

 unlike third. 



Last lower molar simple. 



Dental formula 



I f C 2 Pm I M f 



(In one genus, Pentalagus, MD- 



Enamel usually crenated in reen- 

 trant angles of upper cheek teeth. 



Cutting edge of first upper incisor 

 straight. 



Third upper molar small but 

 usually present (absent in Pentalagus 

 only). 



Second and fifth upper cheek teeth 

 entirely similar to third. 



Last lower molar double. 



