212 PEROMYSCUS. MEGADONTOMYS. 



Measurements. Total length, 252-270; tail vertebrae, 120-135; 

 hind foot, 25-27; ear, 20-21. Skull: basal length, 28.8; occipito- 

 nasal length, 32.4; zygomatic width, 15.6; mastoid width, 13.6; 

 length of nasals, 13; width of nasals, 3.4; length of palatal slits, 6.2; 

 width of palatal slits, 3.2; length of palate to palatal notch, 12.8; to 

 end of pterygoid, 19; length of upper molar series, 5; length of single 

 half mandible, 17.4. (Bangs, 1. c.) 



188. mecisturus (Peromyscus} , Merr., Proc. Biol. Soc. Wash., xn, 



1898, p. 124. 

 GREAT-TAILED MOUSE. 



Type locality. Chalchicomula, State of Puebla, Mexico. Alti- 

 tude, 8,400 feet. 



Geogr. Distr. State of Puebla, Mexico. 



Genl. Char. Size large; tail very long; ears large. 



Color. Above anteriorly gray lined with black, and suffused 

 with fulvous; rump pale fulvous; orbital ring dusky; chin whitish; 

 under parts whitish buff; breast buffy; wrists dusky; hands white; 

 sides of ankles, and the toes white; tail above dusky, paler beneath. 



Measurements. Total length, 249; tail vertebrae, 155; hind foot, 

 24. 



43. Megadoiitomys. 



i.j=|; M.t3 =I 6. 



Megadontomys Merr., Proc. Biol. Soc. Wash., xn, 1898, p. 115. 

 Type Megadontomys thomasi Merriam. 



Size large; ears and tail long, scantily haired; pelage long, soft, 

 and very dense. Skull similar in general to that of Peromyscus, 

 but very large and massive; rostrum and nasals much produced, 

 the latter expanded anteriorly and projecting far beyond incisors. 

 Molars very large and heavy, with short tubercles which wear off 

 when the animal is still young, leaving flat crowns; first and second 

 lower molars with a supplementary narrow enamel loop on each 

 side; third lower molar with three salient and two reentrant angles 

 on each side. Plantar tubercles, 7 ; Mammae, 6; pectoral |^|, inguinal 

 ^. (Merriam, 1. c.) 



KEY TO THE SPECIES. 



PAGE 



A. Above mixed fulvous and black M. thomasi 213 



B. Above grayish brown M. nelsoni 214 



C. Above brownish cinnamon M. flavidus 214 



