Mammals from Tres Marias Islands. 15 



Color. — Upper parts drab brown suffused with pale dull fulvous, purest 

 and strongest on sides of neck ; black rings around eyes broader, and 

 reaching farther forward on sides of nose, than in M. canescens ; median 

 facial stripe huffy fulvous, narrower and more sharply defined than in 

 canescens ; under parts huffy yellow, deepest on throat and breast. In the 

 4 specimens examined there is no white on the tail ; canescens commonly 

 has the terminal part white. 



Cranial characters. — Skull similar to that of canescens but longer, de- 

 cidedly narrower and more slender; brain case more rounded; rostrum, 

 palate, and base of skull between audital bullae conspicuously narrower. 



Measurements. — Type specimen: Total length 270; tail vertebras 167; 

 hind foot 19.5. Average of 3 males from type locality : Total length 285; 

 tail vertebrae 170 ; hind foot 20. 



Remarks. — Five specimens of this pretty little opossum were obtained 

 on Maria Madre Island and present practically no individual variation. 

 Mr. Nelson states that the species was common in the forest on top of the 

 ridge which extends along the middle of Maria Madre Island. 



Oryzomys nelsoni sp. now Nelson's Rice Rat. 



Type from Maria Madre Island, Tres Marias Islands, Mexico. No. 

 89200 cT ad., U. S. Nat. Mas., Biological Survey Collection. Collected 

 May 13, 1897, by E. W. Nelson and E. A. Goldman. Original No. 11022. 



Characters. — Size large (decidedly larger than O. meodcanus) ; tail exceed- 

 ingly long and nearly naked ; ears medium, scant haired and rattier pale ; 

 color yellowish fulvous ; skull large and massive. 



Color. — Upper parts dull yellowish fulvous, slightly darkened on head 

 and back by blackish hairs, becoming pale huffy ochraceous on flanks 

 and thighs ; underparts white, the plumbeous underfill' showing through 

 in places ; tail dark except on proximal J or \ of under side which is pale 

 yellowish ; hind feet scantily haired with whitish hairs. 



Cranial and dental characters. — -Skull very large and massive, increasing 

 in length (but not in breadth) with age ; interparietal very broad antero- 

 P< interiorly. Contrasted with O. meodcanus Allen, the skull is very much 

 larger and heavier (even the 9 being much larger than the rf of meod- 

 canus) ; the rostrum decidedly larger ; the interparietal broader antero- 

 posterior^, and the molar teeth relatively as well as actually much 

 broader. 



Measurements. — Type specimen, <$ ad. : Total length 342 ; tail vertebras 

 190 ; hind foot 38. An adult $ : Total length 320 ; tail vertebra 185 ; 

 hind foot 37. Average of 2 adult males from type locality : Total length 

 343; tail vertebras 190.5; hind foot 38.5. 



Remarks. — Mr. Nelson found this new species living in damp thickets 

 and about springs near the summit of Maria Madre Island, where four 

 specimens were obtained. 



