39^ SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



Skull (pis. Lxxiv, i; Lxxv, 2; Lxxxii ; lxxxiii). — The skull of 

 Macrotolagus is large and slender. It is not arched as in the sub- 

 genus Lcpiis. The nasals are larger and narrower, the brain case is 

 narrower, and the choanse somewhat narrower. The postorbital 

 processes are larger, rather longer than they are in the true Lcpiis, and 

 their posterior angles are always attached to the side of the cranium 

 enclosing large foramina. 



Teeth (figure 44, 11-17). — The groove on the front of the in- 

 cisor teeth in this subgenus may be perfectly simple and not 

 filled with cement as it is in Lepus {Macrotolagus) californius, but 

 more often it is deep and filled with cement as in L. {M.) texianus, 

 where the groove is simple, and in gaillardi, allcui, uierrianii, where 

 the groove is bifurcated internally, and in callofis and aselhts 

 where the grove is trifurcated internally. This is the only group 

 of the Leporid?e in North America that shows this complicated 

 folding of the groove internally, but at the same time some members 

 of it do not show it. When found in a North American rabbit this 

 folding of the groove on the incisor is diagnostic of the subgenus, 

 but when not found it is without significance. 



Vertebral Column. — The length of the neural spines is a little 

 greater than it is in either the subgenus Lepus or Pa:cilolagus. In 

 the latter two it is about three times the length of the centrum in 

 the anterior part of the thoracic series of vertebrae ; in Macrotolagus 

 it is a little over three times the length of the centrum. 



Upper Extremity (pi. xcviii, 2). — The radius is slenderer than 

 in the other members of the genus Lepus and longer than the 

 humerus, while in the other subgenera, the humerus and radius 

 are about equal in length. 



Species belonging to this subgenus, see p. 335. 



Genus SYLVILAGUS Gray 



1867. Sylvilagus Gray, Ann. Mag. Nat. Hist., xx, 3d sen, p. 221. 



1896. Syhilagus ]Mearns, Proc. U. S. Nat. Mus., xviii, p. 551, June 24, 



1896. 

 1899. Sylvilagus AIajor, Trans. Linn. Soc. London, 2d sen, vii, Zool., p. 



514, November, 1899. 



Type. — Sylz'ilagus Horidaiius mallurus (Thomas). 



Geographical Distribution. — In general, North America south of 

 the northern border of the United States and in South America. 



Diagnosis — External and dental characters as in Lepus. Skull 

 essentially like that of Lepus except that sutures of interparietal are 

 always distinct ; the postorbital process is long and narrow, its 



