1914.] 



EEITHKODONTOMYS LEVIPES GROUP. 



65 



Color. — ^Upperparts ochraceous-salmon, sparingly mixed on back 

 with black; general tone of sides between ochraceous-salmon and 

 ochraceous-orange ; underparts strongly suffused with light pinkish 

 cinnamon; fore and hind feet grayish white, sometimes tinged with 

 the color of the sides; ears pale fuscous, with ochraceous hairs on 

 inner surface; tail pale fuscous above, grayish white below. Com- 

 pared with toltecus, the ochraceous color is more intense, there is 

 much less darkening on the middle of the back, and the underparts 

 are more intensely buffy. 



SkuU. — About the size of that of R. /. toltecus but shorter and 

 broader; braincase rather flat; zygomata narrowed anteriorly ; nasals 

 short; ascending arms of premaxillse extending about 1 mm. beyond 

 I end of nasals; audital bullae very small; interpterygoid fossa broad; 

 palatal foramina short and widely open. First and second upper 

 molars with accessory enamel loops in primary reentrant angles. 



Measurements. — Average of 3 adults from type locality: Total 

 length, 190 (188-192); tail vertebrae, 110.5 (110-111); hmd foot, 

 20.8 (20.5-21). Skull: (See table, p. 81). 



Remarlcs. — This species is remarkable not only for its peculiar 

 characters but because of its (seemingly) restricted range. It resem- 

 bles somewhat in color and character of pelage certain members of 

 the fulvescens group, but its skull characters place it in the subgenus 

 Aporodon. It seems to be most nearly related to the much larger 

 liirsutus, known only from Ameca, Jalisco. 



At the type locality of levipes occurs another much smaller species — 

 R. fulvescens tenuis — a member of the tjrpical subgenus. In the series 

 referred to this species are three specimens which combine in a 

 remarkable manner the characters of the two species. Externally 

 they differ very little from levipes except in being somewhat less 

 intensely ochraceous, both above and below, and in having rather 

 shorter tails (103 and 104 mm.). Their skulls, however, are decidedly 

 narrower than those of levipes and about intermediate in size between 

 skulls of the latter and of tenuis. The upper molars have small acces- 

 sory tubercles present in the principal angles, but the enamel pattern 

 is practically the same as in tenuis. Another much smaller (adult) 

 skull in the series shows a strong tendency to develop the accessory 

 enamel loop characteristic of the subgenus Aporodon. This skuU 

 (No. 88056, U. S. Nat. Mus.) is smaller than those of typical tenuis. 

 Anomalous as this situation may be, there seems to be no other expla- 

 nation than that these specimens are hybrids between levipes and 

 tenuis. 



Specimens examined. — Three, from type locality. 

 28657°— 14 5 



