Vol. V] TAYLOR— NEW SUBGENUS OF PHENACOMYS J33 



sion, as given in the tables of measurements, is less in albipes 

 than in any specimen of these species measured, with one 

 exception, an example of intermedins (No. 174431 )j in which 

 the dimension is the same as that in albipes. In width of 



C Cranial measurements comparative of 

 Phenacomys (Arborimus) albipes and Phenacotnys (Phenacomys) 



intermedins 



(All measurements in millimeters) 



Width of 

 cranium 

 outside 

 external 

 Greatest Zygomatic Interorbital auditory- 

 Museum length width constriction meatus 



No. Sex Species Phenacomys albipes 



97236 $ 25.6 13.8 3.3 11.3 



797 5 25.1 3.7 11.2 



Phenacomys intermedins 



174431 $ 23.8 13.8 3.7 11.0 



174425 9 24.9 14.2 3.6 11.0 



174432 ? 24.3 14.3 3.7 11.1 



interorbital constriction one specimen of albipes. No. 97236, 

 agrees with longicaudus, while the other. No. 797, is closer 

 to intermedins and orophiliis; in width of cranium outside of 

 external auditory meatus the examples of albipes are less than 

 those of oropJiiliis but greater than those of intermedins. 

 Eight of the nine comparable specimens of longicaudus ex- 

 ceed albipes in this measurement. 



Back upper molar in albipes has the outer portion of the 

 posterior crescent closed off to form a second outer triangle. 

 In the type (No. 97236), the second outer triangle is closed 

 off from the inner portion of the crescent in this tooth on both 

 sides. In the second specimen (No. 797), there is a tendency 

 for the second outer triangle on the left hand side to open 

 very narrowly into the interior part of the crescent. In this 

 character albipes is closest to longicaudus. The inner loop 

 is intermediate in position and outline between orophilus and 

 longicaudus, tending, in No. 97236, in the direction of oro- 

 philus, and in No. 797 in the direction of longicaudus. 

 Whereas in the type (No. 97236) the triangles and loops 

 of the front lower molar are for the most part closed off from 

 one another, in No. 797 they tend narrowly to intercommuni- 

 cate. The tight closure of these loops and triangles is observed 

 often in, if not characteristic of, the subgenus Phenacomys, 



