Osgood — Four New Pocket Mice. 21 



Charactevs. — Size nearly equalling i\vAi oi P.p. siccus ; color paler; mas- 

 toids smaller. Size decidedly greater than in P. p. arenarius; color aver- 

 aging paler; skull larger and heavier; mastoids relatively smaller. 



Color. — Much as in arenarius, hut averaging paler ; paler than in siccus, 

 and not exhibiting a gray phase. General etfect of upperparts ecru drab ; 

 basal partof hairs of upperparts pale gray (Ridgway, PI. II, No. 9) slightly ' 

 tinged with fawn ; no obvious lateral line ; underparts creamy. 



>,%ii//.— Similar in general to that of siccus, but mastoids smaller; larger 

 and heavier and with relatively smaller mastoids than that of aroinrius. 



Measurements. — Average of nine topotypes : Total length, 181 (171-188) ; 

 tail vertebrae, 105 (100-113); hind foot, 24 (23.5-25.5). Skull of type: 

 Greatest length, 26.1 ; basilar length, 18; mastoid width, 13.2; zygomatic 

 width, 13. 1 ; interorbital constriction, 6.6; nasals, 9.4 ; interparietal, 7.3 

 X 3.8 ; diastema, 6.4 ; maxillary toothrow, 3.8. 



Remarks. — This form may be distinguished from both art'ii<trii(s»,nd siccus 

 by its relatively small mastoids. Specimens from Magdelena Island, which 

 lies near Margarita Island, do not approach this form in size or cranial 

 characters, Vjut, though rather pale, seem referable to arenarius, tlie coloi' of 

 which is subject to local variation. 



Perognathus spinatus magdalenae subsj). ntjv. 



Type from Magdalena Island, Lower California, Mexico. No. 146,102 

 U. S. National Museum, Biological Survey Collection. $ adult. Novem- 

 ber 25, 1905. E. W. Nelson and E. A. Goldman. 



Characters. — Size and color nearly as in P. s. peninsulae; mastoids smaller; 

 rostrum slightly longer. Mastoids as in P. s. margaritae ; size smaller; ros- 

 trum longer and broader. 



Color. — Practically as in peninsulae and margaritae, but somewhat more 

 deeply vinaceous ; upperparts fawn color mixed with dusky chietiy dis- 

 posed as fine lines ; lateral line very narrow, fawn color ; underparts 

 creamy white. 



Skull. — Size about as in peninsulae ; mastoids smaller ; rostrum slightly 

 longer; mastoids as in margaritae ; rostrum, nasals, and skull throughout 

 more elongate. 



Measurements. — Average of ten topotyj^es : Total length, 194 (188-200) ; 

 tail vertebrae, 115 (110-122); hind foot, 24(23.5-25). Skulls of type and 

 one topotype, respectively: Greatest length, 26.4; 26.8; basilar length, 17.9; 

 18; mastoid width, 12.6; 12.7; zygomatic width, 12.8; 12.7; interorbital 

 constriction, 6.9 ; 6.7; nasals, 10.5 ; 10.6; interparietal, 8.1 x 3.6 ; 7.5x3.3; 

 diastema, 6; 6.5; maxillary toothrow, 4.3 ; 4. 



Remarks. — This is a slight form which, but for its insularity, might be 

 overlooked. It differs from peninsulae and agrees with margaritae in the 

 small size of the mastoids. In the light of extensive material from the 

 Peninsula, it appears that this form and also the previously described insu- 

 lar forms P. s. margaritae and P. s. brija)iti should be considered only as sub- 

 species, for, though the insular forms are constant in character, variation 

 among mainland specimens is considerable. 



