o 



simplicity of the enamel boundaries of the lakes as compared with the 

 same portions of H. speciosum, with which it agrees in size. The only 

 plications to be observed are the usual opposite ones entering the lakes 

 from the middle of their adjacent boundaries, and a slight one at their 

 inner angle of the same border of the anterior lake. The inner crescents 

 are united, the posterior retaining its width posteriorly and giving off 

 the posterior inner column from its anterior half. Both the internal 

 columns are longitudinally oval and rather small, the anterior well sep- 

 arated. The adjacent enamel border gives oif the usual projecting fold. 

 Outline of crown nearly quadrate. 



A second molar, less worn, presents therefore a little greater com- 

 plexity of enamel folds. Thus the anterior inner part of each lake is 

 folded into a loop, and there is a second pair of opposite folds outside 

 the usual pair on the adjacent borders of the lakes. 



A third molar is much more worn than either of the preceding, so as 

 to throw the inner and median posterior areas together. The anterior 

 median is well isolated and subround. There are no folds of the en- 

 amel plates whatever. 



m. 



Length No. 1 from roots 0.27 



Width of anteroposterior 019 



Width of exterointerior 020 



Length Ko. 2. 032 



Width of anteroposterior. . . . .' - . 021 



Width of exterointernal - 018 



Length No. 3 - 018 



Width of anteroposterior - .021 



Width of exterointerior 022 



From the neighborhood of the Pawnee Buttes, Colorado, 



Protohippiis labrosus. Sp. nov. 



Having obtained a number of fragmentary and entire crania referable 

 to species of the present genus, it becomes possible to correlate the man- 

 dibular with the maxillary forms, dentition, etc., as it has not been pos- 

 sible to do heretofore. Of mandibles there are four types, which refer 

 to species as follows : Symphysis, flat, shallow ; no diastema between 

 their incisor and canine teeibh ; P. labrosus. A diastema, in front of 

 canine ; symphysis narrower, deep ; inferior molars smaller ; F. sejunctus, 

 Symphysis narrow, deep, contracted, and smaller; lower molars larger; 

 P. perditus. 



These comparisons are instituted on one mandible of the first, two 

 entire and three incomplete ones of the second, and two of the third 

 types, all but two accompanied by superior molars or crania. 



The specimen of P. labrosus embraces also the right maxillary bone, con- 

 taining five molars ; a second si>ecimen includes three superior molars 

 of the left side; it is also represented by several isolated molars. 



ProtoMppus labrosus resembles the two species described by Leidy as 

 Merychippus, in the short crowns and long roots of- the molar teeth, 

 with thickened external ridges separated by thin bands of cementum. 

 It therefore differs from VrotoMppus perditus and P. placidus^ resembling 

 the first named in size. It is exactly intermediate between the P. insignis 

 and P. mirabilis in size, and to it is no doubt to be referred Dr. Leid;y's 

 No. 4 of the latter.* Either there are three species of the present char- 



" Ancient Fauna Dakota and Nebraska, p. 300; figured pi. xvii,figs. 8-9. 



