118 Merriam American Wood Rats. 



Rostrum of moderate length, never more than one-third the length 

 of cranium ; sagittal area usually rounded, the broadest part always con 

 siderably anterior to plane of interparietal, whence the sides curve gradually 

 backward to interparietal shield ; spheno- palatine vacuties always open. 



(1) Neotoma leucodon group. Neotoma leucodon, latifrons, micro- 

 pus, baileyi, floridana and pennsylvanica form a fairly well cir 

 cumscribed group, differing from the other subdivisions of the 

 genus in having the f rentals abruptly spreading and flattened 

 immediately behind the intcrorbital constriction, the orbital mar 

 gins upturned and pinched in, almost forming a bead ; the nasal 

 bones short and cuneate, tapering evenly to a dull point behind ; 

 the postpalatal notch moderately or broadly excavated (moder 

 ately in leu-cndon, very broadly in floridana) ; the upper molar 

 series very much broader anteriorly than posteriorly (m - 1 nearly 

 i broader than m -) ; m 1 comprising three transverse loops, the 

 anterior of which is but slightly indented by the antero-internal 

 sulcus never divided by the deepening of this sulcus as in the 

 mexicana series; color of teeth white or nearly white (except in 

 floridana, which is an aberrant member of the group*). N. 

 pennsylvanica has certain primitive characters not shared by the 

 others, and is more nearly intermediate between the subgenera 

 Neotoma and Tcononia than any known living species. The 

 group inhabits the Lower and Upper Sonoran Zones, from 

 Perote in Vera Cruz and Berriozabal in Zacatecas, northward to 

 southern South Dakota. 



(2) Neotoma mexicana, group. Neotoma mexicana'f, pinetorum, 

 orizabse tenuicauda, fidviventer, fallax and fuscipes form a group of 

 closely allied species agreeing in certain important cranial char 

 acters whereby they differ from all the other subdivisions of the 

 genus. N. fu.xci-pc*l and fallax are somewhat aberrant members 

 of the series. Neotoma torquata Ward probably belongs here also . 

 The group seems to occupy a midway position in the genus, lack 

 ing the more specialized characters that distinguish the others. 



*In most species of Neotoma the osteodentine is dark and the reentrant angles are 

 filled with a blackish substance. 



fOtie subspecies of mexicana is here recognized : N. mexicana bullata from the Santa 

 Catalitia Mts. in Arizona. 



JThe subspecies of fuscipes here recognized are macrotis Thomas from the southern 

 coast region of California ; streatori from the western slope of the Sierra Nevada and 

 adjacent parts of the upper Sacramento Valley, and dispar from the east foot of the 

 Sierra along the western edge of the Mohave Desert region. N. monochroura Rhoads 

 and N. splendens True seem to be typical fuscipes, and N. macro/is simplex an inter- 

 grade. 



