128 Proceedings of the Biological Society of Washington. 



Measurements. — Type: Total length, 220; tail vertebrae, 118; hind foot, 

 27. Skull (type): Greatest length, 26.3; zygomatic breadth, 14; interor- 

 bital breadth, 4.9; length of nasals, 10.1 ; length of anterior palatine fora- 

 mina, 4; length of palatal bridge, 5.5; length of upper molar series, 3.8. 



Remarks. — Six specimens from the type locality represent a form 

 apparently allied to 0. melanotis, of Jalisco, but specifically distinct. 

 The wholly black ears and remarkably flat skull are distinguishing char- 

 acters. 



Oryzomys nitidus alleni subsp. nov. 



Type from Tuis (about 35 miles east of Cartago), Costa Rica. No. 

 tItt) young adult male (teeth slightly worn), American Museum of Nat- 

 ural History, collected by George K. Cherrie, July 15, 1894. 



General characters. — In external appearance closely resembling Oryzo- 

 mys nitidus nitidus, the pelage long and very soft as in that form (hairs 

 on back about 12 millimeters in length); skull with higher, much more 

 fully expanded braincase. 



Color. — Type : Upperparts between ochraceous-tawny and cinnamon- 

 brown, purest on cheeks, shoulders and sides; the face, top of head, and 

 back heavily mixed with black, the very dark basal color of the fur 

 showing through and producing a blackish effect ; underparts dull whit- 

 ish; ears black, thinly clothed with very short inconspicuous hairs; feet 

 fiesh color; tail nearly unicolor, dark brownish above, slightly paler 

 below. 



Skull. — Similar in general to that of 0. n. nitidus, but braincase much 

 more distended ; interorbital constriction about the same, but supraorbital 

 ridges more strongly divergent and frontal region decidedly broader pos- 

 teriorly ; dentition about the same. 



Measurements. — Type: Total length, 218; tail vertebrae, 111; hind 

 foot, 29. Skull (type): Greatest length, 28.2; zygomatic breadth, 14.3; 

 interorbital breadth, 5.5 ; length of nasals, 10.9 ; length of anterior pala- 

 tine foramina, 3.5; length of palatal bridge, 5.5; length of upper molar 

 series, 4.3. 



Remarks. — Specimens from San Javier and Carondelet, northern Ecua- 

 dor, some of which have been identified by Mr. Oldfield Thomas with 

 the Peruvian form described as ' Hesperomys laticeps var nitidus ' have 

 been used for comparison. The Costa Rican animal agrees with these in 

 many essential respects ; it differs most noticeably in the expansion of 

 the braincase, the swelling extending forward between the orbits and 

 resulting in a greater lateral development of the frontals. 



The new form is named for Dr. J. A. Allen, of the American Museum 

 of Natural History, to whom I am indebted for many courtesies. 



Specimens examined. — Three, from the type locality. 



Oryzomys alfaroi dariensis subsp. nov. 



Type from Cana, eastern Panama (altitude 2,000 feet). No. 178,660, 

 female adult, U. S. National Museum (Biological Survey Collection), 

 collected by E. A. Goldman, March 4, 1912. Original number 21,453. 



