298 PROCEEDINGS OF THE NATIONAL MUSEUM vol.83 



The fossettes are relatively large and usually simple. The plica- 

 tions on the metaloph between the fossettes are commonly small 

 and numerous in very early stages of wear, but markedly reduced or 

 obliterated in moderate wear. A slight pli prefossette may persist 

 in some specimens in advanced wear. Moreover, a single or double 

 pli prefossette may persist longer in P^ than in other teeth. The 

 posterior fossette plications on the metaloph in some instances are 

 fewer and somewhat larger. A single or double pli postfossette may 

 persist longer than the pli prefossette, though usually an early reduc- 

 tion takes place as on the anterior wall of the metaloph. The pli 

 protoloph and pli protoconule in the anterior fossette are noticeably 

 developed in early wear. The pli protoloph is early reduced in the 

 molars but in the premolars is very persistent and may be double or 

 triple as in no. 11989. In P^ the protoloph unites with the anterior 

 style of this tooth in two places isolating a small lake (fig. 21, no. 

 12543), which may persist untU the tooth is moderately well worn. 

 The pli protoconule though not heavy is apparently the most persist- 

 ent plication in the anterior fossettes and can be seen in teeth of 

 advanced wear. It is difficult to determine whether this plication 

 arises from the crochet or protoconule, certainly very near the junc- 

 tion of the two. It may be single or double, and in a few teeth it is 

 found to be triple (fig. 21, no. 12576). The pli hypostyle is not well 

 developed in most of the specimens and like the pli protoloph is much 

 reduced in the molars except in some specimens in early wear where 

 the premolars are in the stage of eruption. In M^ a prominent 

 plication may arise from the posterior wall of the postfossette (fig. 21, 

 no. 12576 and no. 12546), but this region of M^ is very irregular and 

 occasionally the posterior fossette is open in advanced stages. The 

 pli caballin extending into the postprotoconal valley is best developed 

 in P^ and P^ and may be long and slender in early stages of wear but 

 reduced to a greater extent than the pli protoconule with moderate 

 wear. In many dentitions the pli caballin is only feebly developed 

 in the molars and perhaps early obliterated or reduced to a very 

 slight plication, which may persist to advanced wear. 



The appearance of the protocone varies considerably \vith wear and 

 between teeth in the same dentition. In early wear the pattern is 

 sharply triangular, uniting with the protoconule after the initial 

 truncation of the column. The sides of the triangle are nearly straight 

 at first, although in some teeth the lingual wall of the column shows a 

 shallow groove nearly as in Equus, though generally more subdued. 

 Unlike Erpius this wall in many cases may be noticeably convex, as in 

 specimen no. 12573. With moderate wear the postero-external wall 

 exliibits a simple convexity. The antero-external wall in early stages 

 of wear is generally straight and generally remains more nearly so in 

 the premolars. In M' and M^ the anterior extremity approaches in 



