Vol. 32, pp. 161-162 September 30, 1919 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



A NEW COTTON RAT FROM ARIZONA. 

 BY A. BRAZIER HOWELL. 



In my collection are two cotton rats from the vicinity of Fort 

 Lowell, Arizona, which could not be satisfactorily identified 

 with the material at hand. Accordingly, I sent one of them to 

 the Bureau of Biological Survey for determination, and Dr. 

 Jackson, who examined it, informed me that it probably be- 

 longed to an undescribed race. D. R. Dickey generously loaned 

 me two skins which he had from the same section, and with ten 

 specimens of various Arizona races kindly furnished me by the 

 Biological Survey, through Mr. E. W. Nelson, and a good 

 series of Sig?nodon eremicus in my own collection, the differ- 

 ences appear to be entirely sufficient for me to designate a new 

 form which may be known as 



Sigmodon hispidus cienegae. 



CIENEGA COTTON RAT. 



Type from Bullock's Ranch, four miles east of Fort Lowell, Pima County, 

 Arizona. No. 1531, collection of A. B. Howell; collected by L. M. Huey; 

 January 4, 1916. 



Geographic distribution. — Probably the small and widely scattered ciene- 

 gas and grassy damp spots of the upper Santa Cruz River system. 



General characters. — Closest to Sigmodon h. confinis, but skull with more 

 inflated braincase, larger bullae, and rostrum shorter and wider. Tail 

 slightly shorter than eremicus, and foot considerably longer than that form 

 or confinis. 



Color. — Darker and slightly browner than eremicus, but hardly compara- 

 ble in this respect with specimens of confinis or arizonae, as all of the latter 

 are summer skins. 



Skull. — In comparison with confinis, the skull differs in having slightly 

 larger molars, bullae larger and more globular, inter-orbital width greater, 

 braincase more inflated, rostrum shorter, wider and heavier in general. From 

 31— Proc. Biol. Soc. Wash., Vol. 32, 1919. (161) 



