412 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



all the rabbits examined and consequently has the smallest skull. As 

 a whole the skull is short and wide, arched antero-posteriorly. The 

 brain-case is inflated. 



The postorbital processes are small and slender, free both in 

 front and behind, forming anterior and posterior notches with the 

 cranium proper. 



The interparietal bone is distinct. 



The bony palate is shorter than in any other genus, its least 

 length being equal to twice the length of m\ Its extreme posterior 

 edge only is formed by the horizontal plates of the palate bones. 

 The incisive foramina are wide, the wddest part of each one nearly 

 equaling the length of the bony palate. The distance between the 

 vertical plates of the palate bones is relatively as great as it is in 

 Lcpiis, and much exceeds the length of the bonv palate. 



The zygoma is deep and thin, only slightly expanded at the antero- 

 inferior angle. The posterior free extremity of the malar is moder- 

 ately enlarged. The foot-like extremity of the zygomatic process 

 of the squamosal is rather short, but not relatively so short as it is in 

 Lcpiis. 



The audital bullae are much inflated and the external auditory 

 meatus is very large and rounded. 



The mandible has the general form of the mandible of Lcpiis, but 

 the angular process is relatively smaller and its edge is nearly 

 straight. 



Tccfh (pis. xci, I ; fig. 44, i). — Brachylai^iis has the simplest teeth 

 of any of the Leporidse available for examination. The enamel lacks 

 much of the folding and the crenation found in the other genera. 

 The first upper incisor has a simple groove, not filled with cement. 

 The first upper premolar is very simple, presenting a single reentrant 

 angle instead of the usual three on the anterior face. The infold- 

 ing of the enamel on the inner sides of the four upper molariform 

 teeth extends as far as the middle of each tooth only and lacks the 

 crenation so distinctly seen in the case of the other genera. The 

 anterior lower premolar is also simple. It is divided into an anterior 

 and a posterior portion by a single deep reentrant angle extending 

 in from the external face. It has no infolding of the enamel in 

 front, none on the inner side of the anterior half of the tooth, and 

 a single wide, shallow infolding on the outer side of the anterior 

 portion of the tooth. The posterior transverse portions of the 

 three lower molariform teeth are relatively much shorter than they 

 are in any of the other Leporidas. The lateral length of each pos- 

 terior portion is equal to about half the lateral length of the anterior 



