VERTEBRATE REMAINS, PORT KENNEDY BONE DEPOSIT. 205 



There are always two on the external side ; but the posterior outer may be pro- 

 longed to the inner side, or this prolongation may be cut off into a distinct triangle. 

 These divisions include the following species : 



A Second inferior molar, triangles, f 1 . 



1. Second superior molar, triangles, If Agricola Blasius. M. agreslis, Europe. 



2. Second superior molar, triangles, If 1 Myonomes Raf. M riparius, E. N. 

 Amer. ; M. principalis N. W. N. Amer. 



3. Second superior molar, triangles, If Microtus Selys (= Herniotomy's 

 Selys, Paludicola Bias. Tetramerodon Rhoads). M. amphibins ; M. nivalis ; 

 M. ratticeps ; M. campestris ; M. arvalis ; M. subterraneus ; M. savii, Europe ; 

 M. .rant hognat litis ; M. iownsendii ; M. arvicoloides, N. Amer. ; M. diluvianus ; 

 M. speothen ; M. sigmodus ; M. involutus, extinct, N. Amer. 



A A Second inferior molar, triangles, If 1. 



4. Second superior molar, triangles, If Pitymys McMur. M. pinetorum, 

 N. Amer. ; M. dideltus, extinct, N. Amer. 



The species found in the Port Kennedy deposit are distinguished as follows : 



I. M T , triangles If + trefoil (Microtus). M-j, triangles If; large; 



M. diluvianus Cope. 



II. M T , triangles If + trefoil ; m^, f 1 (Zsodelta). 



a. First triangle on m^ equal the others. M T with short trefoil ; small.; 



M. speothen Cope. 



III. M T , triangles If + trefoil ; m^-, If 1 {Pitymys). 



a. First triangle on m^ marked by a constriction. M T with long 



symmetrical trefoil, with a triangle nearly cut off at base on each 



side ; m^, If 1 ; small ; M. dideltus Cope. 



aa. First triangle on m^ not indicated. M T with laterally curved un- 



symmetrical trefoil, with a large angle on each side at base ; 



small ; M. involutus Cope. 



Microtus diluvianus is a large species of the typical division of the genus as 



to its dental characters. The other species are nearer in dentition to the group 



Pitymys, M. speothen occupying an intermediate position. Individuals of the genus, 



and especially of the species M. speothen and M. dideltus, are abundant in the Port 



Kennedy fissure. 



Microtus diluvianus Cope, Proc. Acad. Nat. Sci. Phil., 1896, p. 381. [Type No. 144, Mus. Acad. Naf. Sci 



§^ This species of vole was first recognized from the m 1 ^^ of both 



^ sides. Subsequently an m T was obtained by Mr. Mercer, which agrees 

 with the teeth first discovered and throws much light on its affinities. 



I Among other things, this species is distinguished by its superior dimen- 

 sions, which exceed those of any American Microtus and equal those 

 of Anaptogonia hiatidens. 

 The triangle formula of the superior molar teeth is m T If ; m-^ If. 

 Microtus In both molars the triangles are acute and are well closed, and the 

 i uvianub p gterior one presents an angle posteriorly. The lateral keels are f 

 and f . The valleys are wide open below. 



