88 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



arrangement approaches that in the 6-tuberculate genera Nyctomys 

 and Rhipidomys. 



The discovery of a Peromyscus on Mount Pirre materially ex- 

 tended the known range of the genus from the western part of the 

 republic to near the Colombian frontier. The specimens were trapped 

 mainly under logs and among the spreading aerial roots of trees, in 

 the unbroken forest, at from 3,500 feet on the slopes to 5,200 feet 

 altitude near the summit of the mountain. None were taken in 

 numerous traps placed at lower elevations, and the species seems to 

 be limited to the upper slopes of the mountains where it is common. 

 Two young were found in a nest about six feet from the ground 

 behind the expanded base of a palm frond, indicating scansorial 

 habits. The nest was composed of pulverized bark, and plant fibers. 

 Worn places over and under logs mark routes regularly used by the 

 species in moving about on and near the ground. Anthony (1916, 

 p. 366) found this species " the commonest rat of southeastern 

 Panama." Numerous specimens were obtained by him at various 

 elevations from 2,650 feet near the old village of Tacarcuna up to 

 5,200 feet near Mount Tacarcuna. 



Specimens examined: Mount Pirre (type locality), 20; Mount 

 Tacarcuna, 47. 1 



Genus NYCTOMYS Saussure. Vesper Rats 



The members of the Middle American genus Nyctomys are 

 medium-sized mice of a rich yellowish color above. The underparts 

 are white. The tail is about as long as the body, and clothed with 

 rather long hair. In many respects the genus resembles Rhipidomys, 

 but the general color is more yellowish than is usual in that genus, 

 and the tail shorter and clothed with longer hair. The skull is short 

 and broad, with a short, slender rostrum and fully expanded brain- 

 case. The f rontals are much broader than in Rhipidomys, the lateral 

 margins projecting well over the orbits. The first upper molar is a 

 rectangular tooth with six tubercles much as in Rhipidomys, but in 

 the less complete division of the anterior lobe and the reduced size 

 of the anterointernal cusp suggests gradation toward the 5-tubercu- 

 late genus Peromyscus. 



1 Collection Amer. Mus. Nat. Hist. 



