206 VERTEBRATE REMAINS, PORT KENNEDY BONE DEPOSIT. 



Measurements. 



mm. 



| longitudinal ; 9 



Diameters, m±-< anteroposterior; 3.75 



I transverse ; 2.50 



( longitudinal ; 7.5 



Diameters, m- 2 - < anteroposterior ; 3 



(transverse; 2.2 



The in T has lost the greater part of the trefoil, so that I cannot give its form. 

 Its posterior portion is well expanded, giving at least two additional ridges to the 

 crown, so that these read f+. The triangles are closed. At the external or free 

 apex of each, the enamel layer is interrupted from the grinding face to the base, 

 causing the presence of a fine groove. This groove is not apparent in the superior 

 molars, and it may indicate a distinct species, and even genus. For the species the 

 name sulcata may be retained, and the generic name Schistodelta be applied to it. 



Measurements. 



mm. 



f longitudinal ; 8 



Diameters, m T < anteroposterior to trefoil exclusive ; 4 



( transverse posteriorly ; 2 



MlCROTUS SPEOTHEN Cope. 



Arvicola {hodelta) speothen Cope, Proc. Am. Phil. Soc, 1871, p. 87, fig. 13. 

 Arvicola (Pitymys) tetradelta Cope, /. c , 1871, pp. 87-88, fig. 14. 



This species is represented by the entire dentition of the left ramus mandibuli, 

 with a few fragments of the adjacent bone. As already pointed out, its characters 

 entitle it to rank as a distinct section of the genus. Thus the triangles of the inner 

 side of the anterior inferior molar are one less than in any species of the section 

 Microlus. The anterior loop presents two well-marked angular basal areas, while 

 its terminal portion is regularly rounded. That this is not one of the species of 

 Pitymys, in which the basal lobe of the anterior trefoil has been cut off by unusual 

 inflexion of the enamel angle, is demonstrated by the structure of the second molar, 

 which is precisely that of typical Mtcrotus, all the triangles from the posterior being- 

 isolated and alternating, producing the formula, If 0. The third molar has the 

 usual formula 1-1-1, the posterior two lobes being crescentic, the anterior trapezoid. 



Measurements. 



mm. 

 Length, grinding surface inferior molars (no. 1) ; 6.8 



Length, grinding surface 1st inferior molars (no. 1) ; 3.0 



Length, fang and crown 1st inferior molars (no. 1) ; 5.0 



The structure of the molar triangles, i. <?., their acuteness and thinness of enamel 

 induces me to describe here, without any certainty of reference, the suj>erior molar 

 teeth of two individuals found near the same time. The formulae of the superior 

 molars are (1) If, (2) If, (3) If + trefoil with elongate acute basal lobes. This 



