532 GEOLOGICAL SUEVEY OF THE TEERITOEIES. 



The general character of the transverse crests of both kinds of teeth 

 is similar. Each crest is composed of two obtuse lobes, whose diameter 

 is greatest exteriorly, but contracts toward their point of contact on the 

 median line. Their section is therefore pyriform, with the apex inward. 

 In an anterior tooth, the cutting-edges are obtuse and descend from the 

 outer margin to the line of division between them. This line is a nar- 

 row fissure in the anterior tooth dividing the cones for more than half 

 their height. This fissure is similar in the posterier molars, but the 

 cones are more elevated and compressed, and are irregularly lobed with 

 low tuberosities, especially on the posterior face. The outer face of the 

 cone of the last pair is separated from the posterior by a low, vertical, 

 ridge. There is a posterior heel, whose summit is continuous with one 

 of the cones. 



The valleys are open and spreading^as in M. oMoticus, and there ap- 

 pear to have been no intermediate nor accessory lobes or cones. There 

 is a cingulum round the anterior molar, which is strongest behind. One 

 of the cones sends a rib inward and downward to a position on the cin- 

 gulam, which partially incloses a fossa on the outer side. 



Enamel generally smooth. 



The tibial face of the astragalus is convex antero-posteriorly, little 

 concave, and oblique transversely. The inner side is elevated, and also 

 shortened from the back forward, so as to leave a considerable neck for 

 the navicular facet. This is convex and oblique, extendiag nearly to 

 the edge of the tibial face on the outer side. The peroneal face is shal- 

 low, and exhibits a small facet and a fossa. The calcaneal facet of the 

 inner side is much produced inward. The external one is a broad oval. 



Measurements. 



M. 



Lengtli of crown of anterior molar 0.055 



AA^idth of crown of anterior molar * 050 



Elevation of cones of the same 025 



AVidth of valley between apices of the cones 027 



Elevation of cone of posterior molar 042 



Transverse diameter of the same at base of fissure 035 



Long diameter of the astragalus 093 



Transverse diameter of the astragalus 100 



Exterior depth of the astragalus 025 



Interior depth of the astragalus 053 



Transverse width of navicular facet 055 



The anterior molar described has but two transverse crests, but is 

 considerably larger than the two crested teeth in Trilopliodon oMoticus. 

 As the other portions indicate a smaller species, the position of this 

 tooth becomes a matter of question. This point, together with the 

 isolated or conic and furrowed character of the divisions of the crests, 

 with the smaller size, separate it from the common species. It also be- 

 longs to an earlier geological period. From M. mirificus, the wide, open 

 valleys, simplicity of the cones, and larger size distinguish it. 



TBSTUDINATA. 



STYLEMYS, Leidy. 



Stylemys(?) niobeaeensis, Leidy. 

 Abundant. . 



