﻿40 



NORTH AMERICAN FAUNA. 



[Xo. 12. 



wholly unlike those of any other microtine. Dr. Coues's description 

 of the claws of Dlcrostonyx is so interesting that it may be quoted 

 almost entire. He says (Monogr. K. Am. Kodentia., pp. 248, 249) : 



The two middle fore claws attain their maximum of development in winter. In 

 spring and early summer these claAvs do not api)ear very different from those of 

 Mijodes \=.Lemmiis], though averaging larger, more bulbous at base nnderneath, with 

 the terminal portion slenderer, straighter, and sharper. This bulbous portion under- 

 neath grows out simultaueousJy with increase in length and amount of curvature of 

 the main j^ortion of the claw, until it equals or oven exceeds the length of the latter, 

 and is quite as stout, or even stouter, being somewhat broad and pad-like. At this 

 period it runs the whole length of the claw, from which it is separated by a groove 

 along the sides, and by a notch at the end, both of varying depth. The claw then 

 looks nearly like tAvo claws, one underneath the other. The pad would then seem to 

 gradually sever its connection with the main claw by progressive increase in depth 

 of the constriction marked by the lateral groove and terminal notch, as well as by 

 loosening from the base, when it appears like an excrescence ; it is finally lost. Thus 

 the process ajipears to be a periodical one, like the shedding of the horns of rumi- 

 nants, and not continually progressive with age; and would seem to be connected 

 with the particularly fossorial habits of the quasi-hibernating animal that digs gal- 

 leries under ground in which to reside during the cold season, as compared with its 

 freer and more active mode of life in summer. At the period of the maximum 

 development of the claws these equal or surpass half an inch in length. * * * 



General remarks. — Dicrosfonyx is so readily distinguished by its 

 peculiar dentition, highly modified feet, and rudimentary external ears, 

 that it requires no detailed comparison with any other genus. 



While Dlcrostonyx torquatus (Pallas) is the only species now recog- 

 nized, there are doubtless several others. 



Genus PHENACOMYS Merriam. 



1889. Phenacomys Merriam, North American Fauna No. 2, p. 28, October 30, 1889. 



GeograpMc distrihution of type species. — Phenacomys intermedhis is 

 known only from the type locality, Kamloops, British Columbia. 



Geographic distribution of genus. — Boreal IsTorth America j also 

 recorded from the bone breccia of Beremend, southern Hungary, and 

 the Forest Beds of ^^orfolk and Suffolk, England (i^ehring, i^aturwis- 

 senschaftliche Wochenschrift, l^Tr. 28, p. 346, July 15, 1894.)i 



Essential characters : 



Upper incisors without grooves. 



Lower incisors with roots on outer side of molars. 



Molars rooted. 



Enamel pattern characterized by approximate equality of reentrant angles in 

 maxillary teeth and great depth of reentrant angles on inner side of mandibular 

 teeth, 



ni 1 with five closed triangles. 



m 3 with two or three closed triangles, 



1 1 have not seen the original description of the remains from Beremend (described 

 by Nehring in Naturwissenschaftliche Wochenschrift, 1883) . The teeth from the For- 

 est Beds represent an animal which is certainly not Phenacomys. (See note on Arvicola 

 intermedins Newton on page 75.) 



