3^8 SMITHSONIAN MISCELLANEOUS COLLECTIONS fvOL. 45 



li') Incisive foramina, not irianyular in outline, small, their 

 sides approximately parallel, i)ostorbital process larger 

 and blunter. Genus Pcntalagus, p. 428. 

 /") Nasals relatively larger, wider behind than in front. 



/; ) Audital bulla much reduced in size, smaller than foramen 



magnum. Genus Pronolagiis, p. 416. 

 Ii') Audital bulla normal, as large as the foramen magnum. 

 Genus Romcrolagiis, p. 420. 

 e') Postorbital process large with distinct anterior and posterior 

 limbs, bony palate relatively shorter, usually less than its poste- 

 rior third formed by the horizontal plates of the palate bones. 

 /) Interparietal not present as a distinct bone in adult life. Genus 

 Lcpiis, p. 389. 

 j) Skull shortened and arched, posterior limb of i)ostorbital 

 not touching the sides of the cranium. 

 Ic) Size large, postorbital process wide and heavy, nasals 

 and rostrum wider and heavier. Spmes of luml)ar 

 vertebras well marked. Subgenus Lcpiis, p. 394. 

 k') Size medium, postorbital process rather slenderer, 

 nasals and rostrum narrower. Spines of lumbar 

 vertebrae low and triangular. Subgenus l\vcilo- 

 lagus, p. 395. 

 ;") Skull elongated, less arched, posterior limb of postorbital 

 meeting side of cranium and enclosing a large foramen. 

 Subgenus Macrotolagus, p. 395. 

 /') Interparietal present as a distinct bone in adult life. 



/) Choana^ very narrow, pharyngeal vault high, distance be- 

 between vertical plates of palate bones less than least 

 length of bony palate. Posterior limb of postorbital 

 not meeting side of skull. Genus Oryctolagus, p. 402. 

 /') Choanse not remarkably narrow, the distance between the 

 vertical plate of palate bones equal to or greater than 

 the least length of bony plate. 

 in) Skull and rostrum shortened, arched, audital bullre 

 very large. Postorl)itaIs slender, neither its an- 

 terior nor its posterior limb touches the side of the 

 skull. Genus Brachylagiis. p. 411. 

 in') Skull and rostrum not relatively shortened, audital 

 bulhe not greatly enlarged, posterior limb of post- 

 orbital usually in contact with side of the cranium, 

 rostrum heavier. Genus Sylvilagus, p. 396. 

 11) Posterior limb of postorbital always meeting side 

 of cranium, and inclosing a clavate slit nar- 

 rower than llie process itself. Subgenus 

 SylvHagus, p. 401. 

 n') Posterior limb of postorbital not meeting the 

 side of the cranium, or if it does, enclosing a 

 clavate slit as wide or wider than the process 

 itself. Rostrum slenderer. Subgenus Micro- 

 lagits, p. 402. 



