1896.] NATURAL SCIENCES OF PHILADELPHIA. 379 



Study of the specimens shows that M. dissimilis Leidy was founded 

 on inferior canine molars of M. jeffersonii, and that the teeth so 

 named by me are the corresponding teeth of M. xvheatleyi. M. 

 sphenodon was founded on teeth of young individuals of 71/. wheat- 

 leyi. M. loxodon and M. tortulus are sustained as distinct. 



GLIRES. 



Anaptogonia hiatidens Cope. Proc. Amer. Philos. Soc, 1871, p. 91, fig. 18. 



I have described from the Wheatley collection several species al- 

 lied to or belonging to the voles, and in this paper I add two others. 

 These forms are referable to those genera, which are defined as fol- 

 lows : 

 Pulp cavity and lateral grooves closed below ; teeth rooted ; 



Anaptogonia Cope. 

 Lateral grooves and pulp cavities open below ; no roots ; 



MicROTUs Selys. 



The first term in the Microtine series of genera is the genus Anap- 

 togonia, where the crowns of the molars are short at maturity, and 

 there are rather elongate roots. This is naturally the primitive 

 genus, and it is interesting now that two fossil species referable to it 

 have been discovered.^ 



But one species of Anajjtogonia has been obtained from the cave 

 formations of this country, Anaptogonia hiatidens Cope. It is rep- 

 resented by two series of the inferior molars of the right side, a first 

 inferior molar separate, and some superior molars. The prism-for- 

 mulse of these teeth are as follows : (1) 1 six-lobed | 1 ; (2) | 1 ; 

 (3) 111. The first molar is larger than both of the others together. 

 Its triangles | are isolated, but anterior to these, one on each side is 

 well defined, but the dentine is continuous with that of the anterior 

 lobe. This lobe consists of two prominent basal loops, and two less 

 prominent terminal rounded lobes, all unsymmetrical. There are 

 thus six keels on each side of the crown and a rounded front bor- 

 der. The triangles of the M. ^ are acute, and the anterior of the 

 opposite sides are not fully separated from each other, a strip of 

 dentine connecting them. In the M. ^ the triangle of one side is 

 less developed than the other, and the one extremity of the last col- 

 umn is smaller than the other, forming rather a curved process of 

 a terminal triangle of the opposite side. The pulp cavity is well 

 enclosed below, and the two roots are rather small and divergent. 



^See Merriam, North American Fauna, No. 2, 1889, p. 28; On anew 

 Genus and Four new Species of Arvicolina\ 



