552 RABES FROM MEXICAN BOBDEB—MEABNS. vol.xviii. 



aa. Skull and teeth lighter; rostral portion "wider than high ; postorbital pro- 

 cesses united with the cranium behind (in old specimens), inclosing a nar- 

 row foramen; upper surface of skull much less pitted; skull much arched 

 above, sometimes wider than one-half of its length; pelage softer and 

 longer ; feet densely padded ; head, ears, tail, and feet relatively larger. 



Sylvilagns, Gray.' 

 AA. Interparietal distinct only in the fetus, and for a short period after birth ; always 

 obliterated in adults; usually developed from two ossific centers; skull 

 low and narrow, its breadth considerably less than half the length, with 

 large, arching jiostorbital processes, which are united to the cranium by 

 suture posteriorly, inclosing a long and wide foramen; nasal bones long; 

 anterior upper incisors rounded externally, and without a distinct lateral 

 groove. Ear longer than hind foot; tail black above, this color running 

 up on the rump. Pelage never white MacrotoJagits:- 



Tlie species and subspecies oi LepuH at present known to inhabit the 

 region of the Mexican border may be determined by reference to the 

 following key : 



ANALYTICAL KEY TO THE SPECIES AND SUBSPECIES OF LEPUS FOUND ON THE MEX- 

 ICAN BORDER OF THE UNITED STATES, INCLUDING THE LEPUS CALLOTIS, WAGLER, 

 OF MEXICO. 



A. Interparietal persistent as a distinct bone in adults; usually developed from a 



single ossific center. Ear shorter than hind 

 foot (except in L. cinerascens). 



a. Skull aud teeth massive ; superior outline moderately convex ; postorbital pro- 

 cess of frontal bone auchylosed Avith tlie cra- 

 nium for its entire length, "leaving neither 

 foramen, notch, nor suture ; " frontal aud pari- 

 etals deeply pitted; skull about half as wide 

 as long, with the muzzle about as wide as 

 high; pelage harsh; feet scantily clothed; 

 head small ; ears, tail, and hind feet relatively 

 short (= Rydrolagns, Gray ) aquaiicus.^ 



aa. Skull and teeth lighter; superior outline strongly convex posteriorly; post- 

 orbital process united with the cranium behind 

 (in old specimens), inclosing a foramen ; upper 

 surface of skull much less pitted, about as 

 wide as long, with the muzzle usually wider 

 than high ; pelage softer aud longer, especially 

 on the feet, which are heavily padded ; head, 

 ears, tail, and feet relatively larger {=^SyIri- 

 lagiis, Gray). 

 i. Ear longer than hind foot; tailshort; skull narrow, low, and lightly ossified, 



with postorbital process usually free, scarcely 

 touching cranium behind cinerascens. 



' Lepiis cinerascens, Allen, an aberrant species, is provisionally referred to a second 

 section of this subgenus. (See key to species.) 



^Macrotolagus, new subgenus. Type Lepus alleni, Mearus, from southern Arizona 

 and adjacent parts of Mexico. 



^This has recently become Lepus aquaticus aUwateri, Allen, Bull. Am. Mus. Nat. 

 Hist., N. Y., VII, Art. X, November 8, 1895, pp. 327, 328. Type locality : Medina River, 

 18 miles south of San Antonio, Texas. 



