No. 2.] THE RELATIONS OF PROTOCERAS. 307 



The second premolar is much more elongate antero-pos- 

 teriorly than the first and is inserted by two widely separated 

 fangs ; the crown is low and compressed, with trenchant edges, 

 and is of very simple construction. The para- and metaconids 

 are but obscurely developed, and a faint ridge on the inner side 

 of the protoconid encloses an incipient valley. The third pre- 

 molar, like Ai, is the longest (fore and aft) of the series, though 

 the difference is less marked than in the upper jaw. In con- 

 struction it resembles 'p~2, but all the elements are more dis- 

 tinctly differentiated and the posterior valley is deeper. The 

 fourth premolar is shorter and wider than the third and has its 

 component cusps more clearly demarcated ; the deuteroconid 

 is well shown and the ridge which passes backward from that 

 cusp extends to and fuses with the metaconid, so that the pos- 

 terior valley forms a "lake." 



The inferior premolars of Leptomeryx are in general very 

 similar to those of Protoceras, but p~i, which stands isolated by 

 diastemata, is much more reduced, and on the others the an- 

 terior and posterior basal cusps (para- and metaconids) are 

 much more distinct and form sharp elevated points. In Hyper- 

 tragulus pi is wanting, p~2 has a considerable diastema both in 

 front of and behind it, and /j and p~^ are smaller and simpler 

 than in either of the genera mentioned. 



The molars are very low-crowned and have narrow, shallow 

 valleys, which are worn nearly to the bottom at a comparatively 

 early stage of attrition. The crowns are quite broad in propor- 

 tion to their length, which increases regularly from TfTi to JJTj. 

 The internal crescents are thinner and less distinctly conical 

 than in Geloais. In the smaller and more abundant specimens 

 the external pillar is but feebly developed, especially upon l^i, 

 in the largest-sized jaws (perhaps old males) the pillar is well 

 shown ; in such cases it is largest on wj, smallest on liTi. The 

 talon of wj? is large and consists of two elements, which are 

 more or less distinctly separated from each other. In Lepto- 

 meryx the lower molars differ from those described chiefly in 

 their relatively less width and greater height, in the absence of 

 the external pillar, and in the complete separation of the two 

 elements which compose the talon of 'Wj. 



