36 Proceedings of the Biological Society of Washington. 



area, though normally colored animals were captured there also. 

 More extensive collecting will be necessary to determine this 

 point. 



In all twenty rats were trapped, 16 adults and 4 juveniles, 

 the latter being evenly divided between the two colorations, 

 while of the adults 11 were normal and 5 were melanistic. 1 

 regret that no account was kept of the number of normal indi- 

 viduals from the area in which the others were taken, but I did 

 not realize until too late that these latter seemed to be confined 

 to certain limits. 



A more detailed description of the animals is as follows : 

 The underparts of the melanistic examples are nearest the 

 ochraceous buff of Ridgway but somewhat darker than the plate 

 and with a vinaceous tinge; the base of the hair is plumbeous. 

 This color in a somewhat modified shade forms the ground 

 color of the upperparts, but is there given a dusky character 

 by the admixture of black-tipped hairs. The face and top of 

 the head are decidedly dusky, more so, especially the face, 

 than in normal examples. 



The upper part of the tail is black or slate black, shading 

 imperceptibly into slate on the under side. The feet above are 

 dark colored to the base of the toes (in one specimen the toes 

 are dark). This color is now nearest Ridgway 's mouse gray 

 but darker, and my recollection is that in the fresh specimens 

 it was nearer black. 



The melanistic juveniles show the same characteristics, modi- 

 fied by the slaty-blue color of the juvenile coat. These were 

 about half-grown. 



In normal specimens from the same locality the underparts 

 are white, the base of the hair being plumbeous as in the 

 others. The sides are an ochraceous buff closely matching that 

 of the other form, and the back is quite like the melanistic 

 animals, but perhaps a trifle lighter and grayer, and the top 

 of head and face are lighter. As the plates show, the feet are 

 entirely white. The upper surface of tail is black, under white. 

 There is sometimes an ochraceous-buff band on the chest 

 between the forelegs; this is very variable, sometimes lacking 

 entirely, sometimes extending clear across the chest, and vari- 

 ous stages between these two extremes occur. 



In comparing these specimens from San Acacio with others 



