132 University of California Publications in Zoology. [Vol. 7 



Skull. — Like that of M. macrurus but much larger and more 

 robust. I cannot perceive any difference in shape or proportions 

 (see plate 5). 



Measurements. — Type: length 215mm.; tail vertebrae 84; 

 hind foot 25. Average of five adult males: length 216.8 (208- 

 232) ; tail vertebrae 81.6 (76-92) ; hind foot 25.4 (24-26) ; 

 average of sixteen adult females: length 214.5 (203-232); tail 

 vertebrae 83.9 (70-92); hind foot 25.1 (24-26). 



Skull (type) : basal length 27; zygomatic width 17.5; mastoid 

 width 13.5 ; diastema 9 ; nasals 8.5. Average of twenty-one adults : 

 basal length 27.2; zygomatic width 17.6; mastoid width 13.5; 

 diastema 9.3 ; nasals 8.5. 



Remarks. — This is a very distinct species, not requiring close 

 comparison with any other Alaskan meadow-mouse. It is of 

 about the size of M. elymocetes, but belongs, of course, to an 

 altogether different section of the genus. It appears to be a 

 gigantic insular development of M. macrurus, but none of the 

 specimens secured show intergradation with that species. 



We found it only on Coronation and Warren islands, two out- 

 lying and rather isolated islands on the western edge of the 

 archipelago. It was rather abundant in the woods, where deep, 

 well-defined runways intersected the mossy carpet in every direc- 

 tion. These runways generally led from the tangled roots at 

 the base of some old tree to another similar location, and in such 

 places we uncovered several nests, round balls of moss, some 

 eight or ten inches in diamete^f . This apparently was the sum- 

 mer home of the species, for although there were runways and 

 burrows in some little meadows bordering a stream on Coronation 

 Island, the work was all old and the mice had apparently deserted 

 the place. In these same meadows several old nests were found 

 lying on top of the ground, composed of dry grass, and of about 

 the same size and shape as the ones of moss in the woods. 



At the time of our visit to the islands. May 14 to 18 on 

 Coronation, and May 19 to 23 on Warren, no young ones were 

 out yet and I believe that none had been born, though juvenals 

 of M. macrurus had got into the traps several weeks earlier. Most 

 of the females secured contained large sized embryos, from four 

 to seven in number, but no females were taken which were 

 nursing. 



