RICE RATS 275 



rostratus sp. nov. Metlaltoyuca, Puebia, Mexico 

 rostratus 7)iegadoii subsp. 



nov. Teapa, Tabasco, Mexico 



y7icata7tensis sp. nov. Chichenitza, Yucatan 



jfulvescetzs (De Saussure) Orizaba, Vera Cruz, Mexico 



These species fall naturally into four groups, which, from 

 their typical species, may be named the pahistrts-mexicamis , 

 the chafmani, the melanotis, and the fulvescens groups. Two 

 of these, the mexicmms 2indi chapmani ^ro^x^^^ are partly bridged 

 by intermediate forms. 



1. The ■pahistris-7nexicanns group is characterized in the 

 typical forms by rather large size, short ears, large and massive 

 skulls, long incisive foramina, and strongly developed super- 

 ciliary beads. All of the known large species, and a few of 

 medium size, belong to this group. The members may be ar- 

 ranged in two series according to the color of the underparts, 

 as follows : 



{a) White-bellied forms : -pahistris^ natator, ^entnsul<^, albi- 

 venter, cozmnelcB (sometimes pale fulvous), nelsoni, aztectis^ 

 inexicamis (belly sometimes buffy), btilleri^ rtifiis. 



{U) Fulvous bellied forms : aquatictts, cozunielce (usually 

 \^\)SX.€), fidgens ^ crmittis, j'alapce, teapensis, zygomatiais, gold- 

 mam, coziest', mexicmius (belly usually white), mexicamis ^ara- 

 grus, richniondi. 



2. The cha^Tiiani group is characterized by rather small size, 

 dark coloration, and small mouse-like skulls, with only faint 

 superciliary beads. The species are chap?naiii, palatmus, 

 hylocetes, rhabdoj)s, angtistice^s . 



3. The melanotis group is characterized by medium size, 

 large dark ears, and relatively short incisive foramina. The 

 species are melanotis, rostratus, yucatanensis. 



4. T^x^ fulvescens group is characterized by extremely small 

 size, yellowish fulvous coloration, tiny thin and papery, mouse- 

 like skulls, without supraorbital beads, resembling the smaller 

 species of Reithrodontomys . Only one species has been de- 

 scribed. It is smaller than a house mouse, has a yellowish 

 fulvous body, long and slender tail, and rather large black 

 ears. If of larger size it would doubtless be separated into sub- 

 species. 



