Cope.] -^ [April 17 



species. The bones of the limbs are relatively less robust in the II. derbi- 

 anus.* The differences, especially in the humerus, are well marked. 



I name this species in honor of Prof. Orville A. Derby, in charge of the 

 department of Geology in the Museo National of Brazil. 



MAMMALIA. 



TOXODON EXPANSIDENS Sp. nOV. 



The incisors of the first and second places of the upper jaw, represent 

 this species. Comparison with the corresponding teeth of the known 

 species, reveals well-marked distinctive characters. 



The incisor of the median pair has greater transverse, and less antero- 

 posterior, diameter than in any of the known species. Its diameters are 

 uniform. The cutting edge is five and a half times as long transversely 

 as it is auteroposteriorly. The anterior enameled face has two planes, a 

 wide exterior one which is concave, and a narrower inner one which re- 

 treats inwards, and is plane to the convex inner (median) edge. The 

 enamel extends round the narrow external edge, but disappears at the 

 middle of the inner beveled faces. The angle between the two faces 

 forms a rib, parallel with the borders of the tooth. No enamel on the 

 internal face. Enamel surface with rather coarse obsolete longitudinal 

 grooves. 



The external incisor is a robust, prismatic, rodent-like tooth, strongly 

 curved. Its section is triangular, the posterior (enameled) face being 

 convex. The external face is flat, and its plane forms less than a right 

 angle with the anterior face, from which it is separated by a convex inter- 

 mediate surface. The prominence of the latter causes the anterior face to 

 be slightly concave. The angle is the most prominent portion of the cut- 

 ting edge. The enamel ceases a little short of the narrow internal edge 

 of the tooth ; its surface is marked with obsolete longitudinal grooves. 



Measurements of Teeth. M. 



First incisor. 



r vertical 080 



Diameters of crown J transverse 059 



I . . fat middle Oil 



anteroposterior { 



L (- at angle 015 



Width of internal level 022 



Second incisor. 



(vertical on curve 150 

 transverse 033 

 anteroposterior (externally) 021 



This species is as large as the Toxodon platensis Owen. As compared 

 with that animal, the median incisors have much greater transverse ex- 

 tent, and relatively smaller anteroposterior diameter. These teeth are 



♦For figures of humerus and femur of IT. rodgersi, see Transac. Amer. Philos. 

 Soc. xiv, PI. iv, figs. 10-11, 1879. 



