Vol. V] TAYLOR— NEW SUBGENUS OF PHENACOMYS J23 



with anterior, inner and outer loops all broadly communicating, 

 three long inner and two short outer triangles, and a posterior 

 transverse loop. Certain specimens (as Phcnacomys longi- 

 candiis Nos. 19979 and 21150) have the outer loop of the 

 anterior trefoil closed to form an additional outer triangle. 

 In one specimen of longicaudus (No. 42621) both inner and 

 outer loops of the anterior trefoil are constricted to form 

 triangles, though neither triangle is completely closed. The 

 small anterior loop in this specimen bends sharply inward. 

 No. 42621, therefore, has a small anterior loop, four inner 

 and three outer triangles, and posterior transverse loop. 



The species of the genus differ more or less constantly in 

 the tightness of closure of loops and triangles. There prevails 

 in longicaudus the most open condition which I have observed 

 in the genus; in albipes and intermedins the closure is tighter; 

 and in orophilus it is tightest of all. 



No. 21147 is unique among the specimens of longicaudns 

 in having the inner reentrant angles so deep that the second 

 outer triangle is not in evidence. Ordinarily the second inner 

 triangle is closed off from the second outer triangle, while the 

 third inner triangle is not closed. In No. 19983, however, 

 the reverse is true. In one or two examples the molar pattern 

 is slightly different on right and left sides. Teeth which are 

 much worn have the reentrant angles transformed into lakes, 

 and do not show the enamel pattern characteristic of earlier 

 ages. 



In most of the specimens of longicaudus the first inner 

 triangle opens into the outer loop of the anterior trefoil, while 

 in albipes and in a majority of the specimens of orophilus 

 before me it is closed. In three specimens of intermedins a 

 narrowly open condition is observed, but in the type specimen 

 of intermedins, as figured by Merriam (1889, pi. IV, opp. p. 

 44), the triangle is closed. Two specimens of longicaudus 

 (Nos. 21152, 21147) have the first inner triangle closed off 

 from the outer loop of the anterior trefoil. In No. 19983 the 

 triangle is open on one side but closed on the other, and it is 

 only very narrowly open in two or three examples, notably 

 No. 19130. In most young individuals of orophilus the first 



