Rabbits and hares are crepuscular and possibly more nocturnal than diurnal. So far as I know they do not store food as do their diurnal relatives, the pikas. Some leporids, however, have an unusual, and possibly unique, method of processing food: Two types of vegetable pellets are expelled from the anal opening of the digestive tract; the dark brownish pellets, from which the nutriments have been extracted, are feces, but the greenish pellets seem to be only slightly predigested foods which are re-eaten. Southern (1942:553), among others, has written about this. This system functionally resembles that in the ruminants where a cud of vegetation is returned to the mouth, from one part of the stomach, to be re-chewed and finally swallowed.
Because the causative organism of a disease that decimates dense populations of small mammals, and some other kinds of vertebrates, was isolated first in leporids, this disease, tularemia, is more associated in the popular mind with rabbits than with other kinds of mammals. Actually, many kinds of mammals are quite as likely to have tularemia as are rabbits. Now that streptomycin is available, cases of tularemia in persons are easily cured.
KEY TO SPECIES OF THE GENERA SYLVILAGUS AND ROMEROLAGUS
1. Antorbital extension of supraorbital process more than ½ length of posterior extension; first upper cheek-tooth with only one re-entrant angle on anterior face; re-entrant angle of second upper cheek-tooth not crenate _Sylvilagus idahoensis_, p. 139
1´. Antorbital extension of supraorbital process less than ½ of posterior extension or entirely absent; first upper cheek-tooth with more than one (usually 3) re-entrant angles on anterior face; re-entrant angle of second upper cheek-tooth crenate.
2. Anterior extension of supraorbital process absent (or if a point is barely indicated, then 5/6 or all of posterior process fused to braincase).
3. Tympanic bulla smaller than foramen magnum; hind foot more than 74; geographic range wholly in United States.
4. Ear more than 58 from notch in dried skin; basilar length of skull more than 63 _Sylvilagus aquaticus_, p. 166
4´. Ear less than 58 from notch in dried skin; basilar length of skull less than 63.