720 SIX XKJr XOHTH AMKRICAX M.lilMAI.S—ilE.lUXS. 



explorations in western Sonora, and visited Tiburon Island in company 

 with INIr. W J ^IcOee, of the Bareaii <»f Ethnoloiiv, in D('('end)er, 1895. 

 With a meager sni)ply of trajis, Mi-. Mitchell suc(!eeded in capturing 

 two species of small mammals — a IHpodomys and a Pcnnnysviis — both 

 of which differ from the forms found on the adjacent mainland of 

 Sonora. though i)lainly showing that they originated from them. 



Type. — No. G3188, U.S.N.M. (Collection International Boundary Com- 

 mission). Adult female, skin and skull, from Tiburon Island, Gulf 

 of California, ]\rexico. Collected by Mr. J, W. Mitchell, December 23, 

 1893. Original number, 3. 



Description of type. — Similar to Dipodomys merriami simiolHs^ Khoads, 

 but slightly smaller, with much shorter ears and stronger coloration. 

 As in the case of the Tiburon Island mouse, described beyond, the tail 

 is much more heavily coated than that of the cinresponding mainland 

 species; the dark band on its upper aud under surfaces 1)eiug jet black 

 in ]>. niitchelli, mostly light drab in /). )n. siiniolns. The ears are more 

 densely clothed than in J>. m. siiinoliis, and are almost black instead of 

 buffy white. The dark stripe on the under side of the hind foot of D. 

 merriami (typical) is obsolete in the subspecies .simiolus, but in the 

 present si)ecies reappears, and it is intensely black. The body is col- 

 ored like simiolus, except that the sides are more of an ochraceous buff, 

 and the back has more black admixed; the under pelage having a 

 darker slate color. The tail is bushier at the extremity than m the 

 several forms of J), merriami. 



A second specimen (No. 63187, IT.S.N.M., adult male) agrees in size 

 aud coloration with the type. Length of tail vertebra^, 140 mm., hind 

 foot, 38.5; skull, 30.5 by 22.5; nasal bones, length, 13.3. 



Remarls. — I have compared this insular form with Dipodomys merri- 

 ami 7>^e^^<»r^^^', described by Doctor Merriam' from San Jose del Cabo, 

 Lower California, and found it (o be quite different. It is easily dis- 

 tinguished from it by its paler and different coloration, and by the 

 smaller amount of black on the tail. 



PEROMYSCUS TIBURONENSIS, new species. 

 TIBURON ISLAND I)i:Si:irr MOUSE. 



Type. — No. G318(), U.S.N. ]\I. (Collection International Boundaiy (Com- 

 mission). Adult male, skin and skull, from Tiburon Island, Gulf of 

 California, Mexico. Collected by Mr. J. W. ]\Iitchell, December 25, 

 1895. Original number, 1. 



Description of type. — Suuillest of the desert mice, its hind foot meas- 

 uring but 19 mm., and ear from notch, IG; skull, 24 by 12 nun. Color 

 above, drab gray, thickly mixed with black; sides, ochraceous cinna- 

 mon; under parts white; ears purplish black, almost naked; tail (piite 

 densely coated with blackish hairs. Comi)ared with reromyscus eremi- 



' Proc. Ciil. Acad. Sci.. l' sei., Hi, Juue 5, 1893, p. 345. 



