140 Merriam — Little Known Kangaroo Rats. 



and ///(/t'/i.s, the largest of all. Another interesting feature is 

 that in many localities two species occur together, and in several 

 places three may l)e found within a distance of a few miles. 

 The various species appear to he liighly sensitive to climatic 

 conditions, and adhere very closely to definite zone positions. 

 As a result, it is not unconnnon in the (Ireat Basin region to 

 encounter two or three species in ascending from the hottom of 

 a desert valley to the adjacent mountain slopes. The great 

 majority of species helong to the Upper Sonoran zone, of which 

 some inhabit the upper part, some the lower. A few belong to 

 the Lower Sonoran and Transition zones respectively, and one 

 species — montanus of Baird — apparently enters the lower edge 

 of the Boreal. 



Like the other kangaroo rats, the members of the genus 

 Perodlpus are primarily desert animals. A few species inhabit 

 the bare open deserts, but most of them live in the l)i'ushy 

 deserts, and at least two of the California species — sfrcaturi and 

 venustiis — live among the manzanita thickets of the mountain 

 slopes — a very curious place in which to find a kangaroo rat. 

 One of these species, venustus, inhabits the Santa Cruz Moun- 

 tains, and was also obtained l)y the Goldman ))rotliers and 

 myself on the very top of Santa lAicia Peak, in the coast ranges, 

 at an altitude of 6000 feet. 



Note on Perodipus montanus Baird. 



Dipodomys montanus Baird, Proc. Acad. Nat. Sci. Phila., VII, p. .334, 1855. 



Perodipus montanus of Baird is a well-marked species, a little larger than 

 ordi, but decidedly smaller than agilis, longipes, and richardsnni. It was 

 collected by F. Kreuzfeldt on Captain Beckwith's expedition, in San Luis 

 Valley, south central Colorado, near Old Fort Massacliusetts (now Fort 

 Garland), from which point the Biological Survey has obtained a large 

 series of topotypes. By a curious error, Dr. E. A. Mearns has identified 

 the species with Dipodomys elator Merriam of Texas ( Proc. Biol. Soc. W'asli., 

 XIII, 167, Oct. 31, 1900). Fortunately, Baird's type specimen oi mania nvs 

 is still in existence, in the U. S. National Museum. Comparison of this 

 type with the above-mentioned series of topotypes shows them to be iden- 

 tical, and to differ widely from Dipodomys elator of Texas. 



Doctor Mearns may have been misled by the fact that the fifth toe 

 (really the thumb) which distinguishes Perodipus from Dipodomys is not 

 apparent in the type specimen, for the reason that the hind feet were 

 skinned down to the toes and the bones removed. In all other respects it 



