1914.] 



REITHKODONTOMYS MEXICAI^US GROUP, 



77 



Characters. — Size small; similar in color to R. m. goldmani, but 

 brighter; skull much smaller with narrow braincase. 



Color. — Upperparts pinkish cinnamon, sparingly lined on dorsal 

 surface with blackish brown; color brightest on sides next to the 

 belly, sometimes forming an indistinct lateral Hne (as in the fulvescens 

 group); ears dark hair-brown; tail fuscous, slightly paler beneath; 

 fore feet bujffy white; hind feet grayish white; ankles fuscous; 

 underparts white, sometimes with a slight yellowish cast; less white 

 on sides of nose than in mexicanus and goldrmni. 



SlcuU. — Decidedly smaller than that of either mexicanus or gold- 

 mani; similar in size and general proportions to that of difficilis, but 

 differing in the characters of the subgenus; rostrum short and broad; 

 braincase narrow and moderately flat; nasals short; zygomata nearly 

 parallel to axis of skull (much less contracted anteriorly than in 

 mexicanus); palatal foramina very short; bullge rather small. 



The outer wall of the anteorbital foramen, although much nar- 

 rower than in skulls of R. fulvescens difficilis, is relatively broader 

 than in the other members of the subgenus and may slightly exceed 

 the width of the interpterygoid fossa. The subsidiary enamel loops 

 are present on the upper molars, but the accessory tubercles are 

 rather low. 



Measurements. — Type (immature): Total length, 165; tail verte- 

 brae, 98; hind foot, 16. Average of 2 topotypes (immature): 169; 

 100; 18. A somewhat older (subadult) specimen from Yohaltun, 

 Campeche: 191; 113; 20. Skull: (See table, p. 81). 



Remarlcs. — This is the smallest member of the mexicanus group. 

 Externally it bears a striking resemblance to R. fulvescens tenuis j 

 differing chiefly in darker and more nearly unicolor tail and more 

 uniform ochraceous color (less grizzled with black) on the upper- 

 parts. In skull characters the two differ widely, gracilis clearly be- 

 longing in the subgenus Aporodon. 



From R. m. mexicanus, its nearest relative, it differs in much 

 smaller size, paler coloration, and narrower skull. Judging from the 

 very Hmited material at hand, it seems to be specifically distmct 

 from the other members of the group. One specimen from Yohaltun, 

 Campeche, differs from the type series in being somewhat darker, 

 with blacker, more nearly unicolor tail. 



Specimens examined. — Total number, 9, from the following locali- 

 ties in Mexico : 



Yucatan: Chichen Itza, 6;^ Progreso, 1. 

 Campeche: Apazote, 1; Yohaltun, 1. 



1 Four in Collection Am. Mus. Nat. Hist. 



