1´. Hind legs notably larger than forelegs; hind foot more than 40; nasals widest posteriorly; supraorbital process on frontal; six cheek teeth on each side above Family Leporidae, p. 134 2. Interparietal fused with parietals (see fig. 49); hind foot usually more than 105 Genus _Lepus_, p. 170 2´. Interparietal not fused with parietals (see fig. 10); hind foot usually less than 105 Genera _Romerolagus_ and _Sylvilagus_, pp. 137, 138 Family OCHOTONIDAE--Pikas Certain characters in which this family differs from the Leporidae (hares and rabbits) are: hind legs scarcely longer than forelegs; ears short, approximately as wide as high; no postorbital process on frontal; rostrum slender; nasals widest anteriorly; maxilla not conspicuously fenestrated; jugal long and projecting far posteriorly to zygomatic arm of squamosal; no pubic symphysis; one less cheek-tooth above, the dental formula being i. 2/1, c. 0/0, p. 3/2, m. 2/3; second upper maxillary tooth unlike third in form; last lower molar simple (not double) or absent (in the extinct genus _Oreolagus_); cutting edge of first upper incisor V-shaped; mental foramen situated under last lower molar. Genus OCHOTONA Link--Pikas Revised by A. H. Howell, N. Amer. Fauna, 47:1-57, August 21, 1924. 1795. _Ochotona_ Link, Beyträge zur Naturgesch, I (pt. 2):74. Type, _Lepus ogotona_ Pallas. _Characters_.--Five teeth (excluding incisor) in lower jaw; first cheek-tooth (p3) with more than one re-entrant angle; columns of lower molars angular internally; transverse width of any one column of a lower molariform tooth more than double the width of the neck connecting it to the other column. Subgenus PIKA Lacépède 1799. _Pika_ Lacépède, Tableau des Divisions &c., Mamm., p. 9. Type, _Lepus alpinus_ Pallas. 1904. _Pika_, Lyon, Smiths. Misc. Coll., 45:438, June 15. _Characters._--Skull flattened; interorbital region wide; maxillary orifice roundly triangular; palatal foramina separate from anterior palatine foramina. All of the living members of the family Ochotonidae belong to this genus. American pikas all belong to the subgenus _Pika_, which occurs also in Eurasia. The distribution is boreal and the animals live in talus. This broken rock at the foot of a cliff provides interstices in which the animals live and store grass and herbs. These plant materials are cut for food and stacked in piles to dry in the sun, often beneath slabs of rock which protect the hay-piles from rain. Pikas are diurnal, active throughout the year, and have a characteristic call, "chickck-chickck." Young number two to five per litter. [Illustration: FIGS. 1-4. _Ochotona princeps tutelata_, Greenmonster Canyon, 8150 feet, No. 38519 MVZ, ♂, × 1.] KEY TO NOMINAL SPECIES OF OCHOTONA