Family LEPORIDAE 191 



Skulls 



1. Supraorbital processes each with the posterior projection 



well separated from the braincase, fig. 103a, b\ base of 



skull fenestrated 2 



Supraorbital processes each with the posterior projection or 

 extension partly or completely fused to braincase, fig. 103c, 

 d ; base of skull not fenestrated 3 



2. Nasals gradually narrowed from base to near apex; pos- 



terior projection of each supraorbital process narrow, fig. 



103a '.<... domestic rabbit, Oryctolagus cuniculus 



Nasals almost parallel from base to near apex; posterior pro- 

 jection of each supraorbital process broad, fig. 103^ 



white-tailed jackrabbit, Lepus toivnsendii 



3. Each supraorbital process with part of posterior projection 



fused to braincase, leaving a distinct slitlike opening, 



fig. 103c eastern cottontail, Syl-vilagus floridanus 



Each supraorbital process with posterior extension almost 

 entirely fused to braincase, leaving only a small pore, fig. 

 103d swamp rabbit, Sylvilagus aquaticus 



LEPUS TOWNSENDII Bachman 

 White-Tailed Jackrabbit 



Description. — The white-tailed jackrabbit, fig. 104, is much 

 larger than either the eastern cottontail or the swamp rabbit. 

 The upper parts in summer are buffy or brownish gray, in 

 winter white; the under parts are white, except for the throat, 

 which is buff. The ears are long and tipped with black. The 

 tail is white. The hind legs are long, and the feet are well 

 furred. 



Length measurements: head and body 19-20 inches (475-505 

 mm.); tail 4—41/^ inches (100-115 mm.); over-all about 24 

 inches (575-620 mm.) ; hind foot 5^-6 inches (138-153 mm.) ; 

 ear from notch 4—4]4. inches or about 3^ inches dry (96-113 

 mm.). Average weight: about 7 pounds. 



The skull is about 95 mm. (3^ inches) long; the rostrum is 

 greatly fenestrated. The bullae are comparatively large; the 

 interparietal is fused with the parietals (unfused in Sylvilagus) ; 

 and the posterior projection of each supraorbital process is free 

 (not fused to the braincase), fig. I03b. Dental formula: I 2/1, 

 C 0/0, Pm 3/2, M 3/3. 



Life History. — The white-tailed jackrabbit makes its home 

 in open country, where with its large ears it can hear approach- 

 ing trouble from a considerable distance and with its long legs 



