64 



BULLETIN 171, UNITED STATES NATIONAL MUSEUM 



Also M3 is somewhat more robust than is common in the Recent 

 species. 



Microtus pennsylvanicus, the typical microtine form living in Mary- 

 land today, exliibits a more complex pattern in the first lower tooth. 



Figure Z5.— Microtus (or Pitymysl) cf. invoiuius (Cope): Right ramus of mandible (U.S.N.M. no. 12386), 

 lateral and occlusal views (pattern of M3 taken from mandible U.S.N.M. no. 7772). X 3. Cumberland 

 Cave Pleistocene, Maryland. 



Presumably M. pennsylvanicus is to be regarded as possessing a more 

 advanced type of dentition. 



Table 20. — Measurements {in millimeters) of dentition of Microtus (?) cf. 



involutus and M. dideltus 



Measurement 



MkcoUisi't) cf. invoiuius 



U.S. 

 N.M. 



7686 



U.S. 



N.M. 



no. 



12602 



U.S. 



N.M. 

 no. 

 7772 



U.S. 



N.M. 



123G8 



A.M. 

 N.H. 



8699a 



MicTotus{t) 

 didelttig 



A.M. 

 N.H. 



A.M. 

 N.H. 



(type) 



Superior dentition 



I, anteroposterior diameter... 



I, transverse diameter 



M', anteroposterior diameter ' 



Ml, transverse diameter 



M', anteroposterior diameter. 



M', transverse diameter 



M', anteroposterior diameter. 

 M', transverse diameter 



1.2 



1 



2.2 



1.1 



1.6 



1 



1.3 

 1.8 

 1.2 

 1.9 

 1.1 



Inferior dentition 



I, anteroposterior diameter 



I, transverse diameter. 



Ml, anteroposterior diameter 



Ml, transverse diameter. 



Mt, anteroposterior diameter 



Mj, transverse diameter 



Ml, anteroposterior diameter 



Ml, transverse diameter 



Length of lower cheek-tooth series measured at 

 occlusal surface 



1.2 

 0.9 

 2.6 

 1.1 

 1.5 

 0.9 

 1.5 

 0.8 



5.7 



1.2 



1 



2.5 



1 



1.5 



0.9 



1.4 



O.T 



5.7 



1.3 



1 



2.7 



1 



1.6 



1 



1 



2.5 



1 



»1.5 



1 



1.3 

 0.7 



»5.6 



11.5 

 3 

 1.3 



' Anteroposterior dimensions taken at occlusal surface. 

 > Dimension as given by Cope but not verified. 

 •Approximate. 



The Cumberland Cave form corresponds closely in size to the type 

 of Microtus? involutus (Cope) from the Pleistocene of Pennsylvania. 



