148 BULLETIN 99, UNITED STATES NATIONAL MUSEUM. 



This form while agreeing with Otomys oresfes of Mount Kenia in 

 having only six laminse in the last upper molar differs so greatly in 

 other characters that it should not be considered a subspecies of 

 oresfes unless actual intergrading specimens are found. It is much 

 darker in color, has a considerably longer tail, and the skull lacks 

 almost entirely any appearance of the highly arched interorbital 

 region or wide spreading zygomata of orestes. The skull is in fact 

 almost exactly like skulls of the tropicalis group except for small 

 size and the lamina formula. 



OTOMYS TROPICALIS TROPICALIS Thomas. 



1902. Otomys irroratus tropicalis Thomas, Ann. and Mag. Nat. Hist., ser. 7, 

 vol. 10, p. 314. October. (Western slope of Mount Kenia, 10,000 feet, 

 British East Africa; type in British Mus.) 



Specimens. — One hundred and six, including 43 in alcohol, as 

 follows: 



British East Africa: Mount Kenia, west slope (Loring, Mearns). 



These specimens were collected at altitudes ranging from 7,500 feet 

 up to 13,700 feet. 



About haK a dozen specimens from this large series have eight 

 laminae in the last upper molars; the adtlitional lamina small and 

 subcircular. There is considerable variation in specimens of the 

 swamp rat which I have here placed under tropicalis, but I have been 

 unable to sort the material out into two forms. I have mistrusted 

 at times during work on the genus that there is a form represented 

 in the Kenia material which is related to Otomys tliomasi squalus of 

 the Abcrdare range. In the Aberdares the two groups, tliomasi and 

 tropicalis, are perfectly distinct and easily separated, however, a 

 condition which docs not exist on Kenia unless I have been confused 

 by mismatched skulls in the Kenia collection. 



Mearns records the color of the iris in 0. tropicalis as hazel brown 

 and the mammae as two pairs, inguinal, close together. 



OTOMYS TROPICALIS ELGONIS Wroughlon. 



1910. Otomys irroratus elgonis Wroughton, Ann. and Mag. Nat. Hist., ser. 8, 

 vol. 5, p. 207. February. (Elgonyi, Mt. Elgon, British East Africa; 

 type in British Museum.) 



Specimens. — Fifty, from locahties as follows: 



British East Africa: Aberdare Mountains, summit at 11,000 

 feet, 4 (Heller) ; Changongorra, Aberdare Mountains, 5 (Heller) ; 

 Eldoma Ravine, 12 miles north of Ravine Station, 8, including 7 

 in alcohol (Heller) ; Guas Ngishu Plateau, 30 miles north of Ravine, 4 

 (HeUer); Kaimosi, 17, including 2 in alcohol (Heller); Kakumcga, 

 1 (Heller) ; Mount Kenia, west side at 7,000 feet, 1 (Heller) ; Naivasha 

 Plains, base of Aberdare Mountains, 1 (HeUer); Nyeri, 10 miles east, 



