116 Merriam — New Mice from Mexico and Guatemala. 



Skull similar in general to that of Peromyscux, but very large and massive ; 

 rostrum and nasals much produced, the latter expanded anteriorly and 

 projecting far beyond incisors. Molars very large and heavy (the upper 

 series in type species measuring 6.4 mm.), with short tubercles which 

 wear off while the animal is still young, leaving flat crowns; 1st and 2d 

 lower molars with a supplementary narrow enamel loop on each side ; 

 3d lower molar with 3 salient and 2 renetrant angles on each side. Plan- 

 tar tubercles 7. Mammae 6: pectoral \, inguinal §. 



Peromyscus (Megadontomys) thomasi sp. nov. 



Type from Mts. near Chilpancingo, Guerrero, Mexico (alt. 9700 ft.). 

 No. 70142, tf old, U. S. Nat. Mus., Biological Survey Coll. Collected 

 Dec. 24, 1894, by E. W. Nelson and E. A. Goldman. Grig. No 7250. 



Characters. — Size very large; ears large and nearly naked; tail very 

 long (longer than head and body) and nearly naked ; whiskers large and 

 long, reaching shoulders; hind foot very long (34 mm.); pelage long and 

 rather coarse. Similar to nelsoni, but more fulvous. 



Color. — End of nose black ; upper parts from nose to tail fulvous, bright- 

 est and purest on cheeks and sides, darkest and abundantly mixed with 

 black hairs on back; a blackish ring round eye; under parts white, the 

 basal plumbeous fur showing through ; pectoral region in some specimens 

 suffused with salmon-fulvous ; fore and hind feet white ; ankles blackish. 



Cranial and denial characters. — Skull very much elongated, particularly 

 the rostrum and nasals ; nasals produced and expanded anteriorly ; supra- 

 orbital ridges strongly developed ; anteorbital vacuities drawn out on side 

 of rostrum and only slightly notching root of zygoma ; interparietal very 

 large and broad, subtriangular ; incisive foramina very large ; postpalatal 

 notch broad. Molars large with flat crowns (except in young), measur- 

 ing about 6.5 mm.; crown of last lower molar elongate with enamel much 

 convoluted, presenting 3 salient and 2 reentrant angles on each side. So 

 far as known species are concerned, the skull of thomasi requires compar- 

 ison with only a single species— nelsoni. It differs from nelsoni in greater 

 massiveness, in the possession of prominent supraorbital ridges, and in 

 the stronger development of the posterior reentrant angle of thedast lower 

 molar. 



Measurements. — Type specimen : Total length 350; tail yertebrye 188: 

 hind foot 34. Average of 7 specimens from type locality: Total length 

 330; tail vertebra 175; hind foot 32.8. 



Peromyscus (Megadontomys) nelsoni sp. nov. 



Type from Jico, Vera Cruz, Mexico (alt. 6000 ft.). No. 55024, ? ad., 

 U. S. Nat. Mus., Biological Survey Coll. Collected July 10, 1893, by E. W. 

 Nelson. Orig. No. 5202. 



Characters. — Size large; ears large and nearly naked ; tail very long and 

 scantily haired. Similar to thomasi, but darker and less fulvous; skull 

 lacking the supraorbital beads. 



Color. — Upper parts grayish brown, becoming dusky on nose, around 



