476 GEOLOGICAL SUEVEY OF THE TEEEITORIES. 



GYMl^OPTYCHUS, Cope. 



Paleontological Bulletin, No. 16, p. 6. 



This genus is allied to the squirrels, differing as to cranial characters in 

 the structure of the molar teetb. These exhibit in the superior series two 

 crescents on the inner side, connected by transverse yokes with two cusps 

 on the outer ; in thelower jaw the crescents are on the outer, and the cusps 

 on the inner side. The yokes are separated by deep valleys without 

 cementum, which do not wear out so readily as in Sciurus and marmots. 

 It differs from both these genera in its two well-defined crescents in both 

 dental series. It agrees with them in the position of the foramen in- 

 fraorUtale anterius, which is small, inferior, and situated in advance of 

 the dental series. There are four molars, which do not differ materially 

 in structure in both jaws. Two species are known, a larger and a 

 smaller. 



Gymnopttchus teilophus, Cope, Pal. Bulletin, oSTo. IG, p. 6. G. 



nasutus, Cope, loc. cit. 



Inferior molars with two cross-crests and two cingula from the ex- 

 ternal cones ; each posterior crest of a pair terminating in an interior 

 cone. The inner apices of the crescents unite and give origin to a 

 short median cross-crest. First molar narrower • the anterior part of a 

 ranium probably belongs to the same species. The first molar has a 

 subround crown, with four tubercles ; the second is constructed like the 

 corresponding inferior. Muzzle much compressed j nasal bones flat, 

 extending to beyond above incisors. 



Measurements. 



No. 1. 



M. 



Lengtli of interior three molars 0. 0045 



Length of iirst molar 0015 



Diameter of inferior incisor - 0008 



Depth of ramus at second molar 0036 



Length of diastema above - - 0080 



Width of a pre-orbital region 0073 



Width of end of muzzle .0030 



No. 2. 



Length of four molars • 0. 0070 



Length of second molar 0017 



Width of second molar 0015 



Depth of ramus at second molar - 0035 



Width of lower incisor - 0010 



Gtmnoptychus iNHNUTUS, Copc, Pal. Bull., No. 16, p. 6. 



A very small species. Middle pair of molars with the anterior and 

 posterior cross-crests bifurcate, and a short median cross-crest ; only 

 three cross-crests on the fourth, and four tubercles on the first, itamus 

 deep. 



Measurements. 



if. 



Length of inferior molars - C.GO40 



Lengtli of second molar - .- .0010 



Width of second molar 0010 



Transverse diameter of incisor 9"2*^^ 



Depth of ramus at second molar i-^fiO 



Scarcely larger than the house-mouse. 



