Osgood -Thirty New Mice of the Genus Peromyscus. 71 



palatine slits, 5.3x2.2; diastema, 7; postpalatal length, 9.9; upper 

 molar series, 4.1. 



Remarks. This slight form doubtless owes its dark color to its habitat 

 in a more humid region than that of true yacatanicus. Its range is 

 probably limited to the region of the base of the peninsula of Yucatan, 

 as its nearest relatives known from west of that region are the larger and 

 quite different forms of the mexicanus group. 



Specimens examined. Total number 19, all from the type locality. 



Peromyscus allophylus sp. nov. 



Type from Huehuetan, Chiapas, Mexico. Adult female, No. 77,657, 

 U. S. National Museum, Biological Survey Collection, February 21, 1896, 

 E. W. Nelson and E. A. Goldman. 



Characters. Size medium (hind foot 25) ; tail shorter than head and 

 body; ears moderate, scantily haired ; coloration dark ; tail dusky black 

 ish, unicolor, covered with small imbricate scales, much as in Oryzomys ; 

 proximal third of soles of hind feet finely haired ; skull rather long and 

 narrow ; teeth very small. 



Color. Sides mummy brown, deepening toward middle of back, causing 

 a rather distinct median dorsal line of blackish brown ; under parts yellow 

 ish white over slate-color, the latter showing through ; tail dusky black 

 ish, unicolor; a black orbital ring and antorbital spot; feet whitish, 

 scantily haired ; ankles dusky. 



SkuU. Rather long and narrow ; braincase elevated ; infraorbital notch 

 scarcely evident; nasals rather short, slightly exceeded by premaxillse ; 

 no supraorbital ridge ; palatine foramina rather large, longer than bony 

 palate; audital bullee small, smaller than in aztecus or mexicanus; molar 

 teeth very small ; interparietal small. 



Measurements. Type: Total length, 202; tail vertebrae, 95 ; hind foot, 

 25. Skull: Greatest length, 29.8; basilar length of Hensel,22.5; zygo- 

 matic width, 14.5 ; interorbital constriction, 5 ; nasals, 1 1 ; bony palate, 4 ; 

 palatine slits, 6x2.4; diastema, 8.2; postpalatal length, 10.5; upper 

 molar series, 4. 



Remarks. It is difficult to be certain what are the affinities of this pe 

 culiar species. But for the size of its ears and shortness of its tail, it might 

 well pass for an Oryzomys of the 0. chapmani group. Its dark, scaly tail 

 immediately suggests Oryzomys, and the character and color of its pelage 

 bear out the resemblance. Its skull, however, is that of an ordinary type 

 of Peromyscus without any striking characters. It seems probable that its 

 closest relationship is with the mexicanus group, though it might easily be 

 a northern member of some Central American group not yet known. It 

 agrees in some respects with the description of P. gymnotis Thomas, from 

 Guatemala. Another species from southern Chiapas agrees with this 

 description much more closely, however, and for present purposes has 

 been assumed to be identical with true gymnotis. 



8-Pnoc. BIOL. Soc. WASH. VOL. XVII, 1904. 



