NO. 5 MAMMALS OF PANAMA GOLDMAN IO3 



examples of that form, but the larger size, especially noticeable in 

 the skulls, seems to place them with the remainder of the series of 

 vegetus. 



Specimens examined: Boquete (type locality), 27. 1 



Subgenus MELANOMYS Thomas 



ORYZOMYS CALIGINOSUS IDONEUS Goldman 



Panama Dusky Rice Rat 



[Plate 24, figs. 4, 4a] 



Oryzomys idoneus Goldman, Smiths. Misc. Coll., Vol. 56, No. 36, p. 5, 

 February 19, 1912. Type from Cerro Azul, near headwaters of Chagres 

 River, Panama (altitude 2,500 feet). 



The forms of Oryzomys caliginosus range over an extensive area 

 in northwestern South America and northward in Middle America to 

 Nicaragua. Specimens from widely separated regions exhibit the 

 general characters of the species with remarkable constancy and 

 some of the forms now recognized may ultimately prove to be not 

 well founded. O. c. idoneus is much like 0. c. columbianus of 

 northern Colombia from which it is barely recognizable by slightly 

 darker average color and shorter tail. It differs from typical 0. c. 

 caliginosus of Ecuador in paler, more tawny, instead of russet colora- 

 tion. Compared with the more northern form, 0. c. chrysomelas, it 

 is paler and the skull is more constricted between the orbits, the 

 supraorbital borders less projecting laterally. 



" 0. phaeopus" (O. c. caliginosus) was made the type of the sub- 

 genus Melanomys 2 by Thomas, who mentions its short tail and gen- 

 erally Akodont external form, Oryzomyine molars, broad rounded 

 braincase, short muzzle and well-marked supraorbital ridges. The 

 molar crowns are, however, slightly higher than in typical Oryzomys 

 and the lachyrmal articulates mainly with the maxilla. The skull 

 differs also in the lateral expansion of the inner wall of the antorbital 

 foramen whereby the broad, rounded antorbital opening of typical 

 Oryzomys viewed from above is reduced to a shallow notch. 



O. c. idoneus is the most abundant small rodent in the mixed 

 growth of grass, bushes and small trees at 1,800 to 2,000 feet altitude 

 in the Cana Valley and along the bottom of the canyon of the Cana 



1 Fifteen in collection Mus. Comp. Zool. ; seven in Field Mus. Nat. Hist.; 

 five in Amer. Mus. Nat. Hist. 



'The subgenus Melanomys has been raised to generic rank by Allen (1913, 

 P- 533) but owing to close agreement with typical Oryzomys in dentition and 

 other essential characters such generic recognition seems of very doubtful 

 advisability. 



