76 



AMERICAN MESOZOIC MAMMALIA 



YPM- !oee3 



Fig. 30. Melanodon oweni. Right upper M^"^, crown view. Type. 

 Thirteen times natural size. 



conical. The anterior face is formed by the vertical anterior shearing edge of the tooth 

 and the posterior face is rounded. There is a prominent and sharp ridge, totally absent 

 in Herfetairus arcuatus, running from the internal cusp directly outward across the 



middle part of the crown to 

 the centroexternal cusp and 

 up the latter to its apex. On 

 M^ this ridge seems to bear a 

 very slight prominence at the 

 base of the latter cusp. The 

 raised posterior rim of the 

 crown bears a large interme- 

 diate cusp, as in Herfetairus, 

 but here it is not subcrescen- 

 tic, but semiconical like the 

 anterior intermediate cusp just described. It is nearer to the internal cusp and between 

 it and the posteroexternal cusp the sharp basin rim undulates slightly so that there 

 may appear to be one (M^ M^) or two (M**) tiny cuspules, which would be immedi- 

 ately obliterated by wear. The posteroexternal angle of the crown bears two distinct 

 and nearly equal cuspules. The more posterointernal one marks the end of the posterior 

 crest from the internal cusp and posterior intermediate cusp. The other is connected 

 by a slight anteroexternal ridge to the centroexternal cusp and has also another similar 

 slight ridge external to this which passes onto the base of the centroexternal cusp and 



quickly disappears. The latter cusp is itself unusually 

 developed. It is quite as high as the internal cusp and 

 rather more bulky. Although nearly conical, three 

 small sharp ridges or angulations, already described, 

 run from its apex, one anterointernally, one directly 

 internally, and one posteroexternally. The anteroex- 

 ternal angle of the tooth is formed by a small out- 

 jutting cusp, excluded from the rim of the basin. It 

 is crescentic, the concavity posterointernal, facing 

 toward the body of the crown. 



Measurements 

 Widths of molars of type : 



Outside 



/nsi'de 



Fig. 31. Melanodon. Diagram of typi- 

 cal left upper molar from all aspects. 



Melanodon goodr'ichl^ new^ species 



Type. — Y.P.M. No. 13738. Part of right max- 

 illa with W\ 



