THE MAMMALIA OE THE DEEP RIVER BEDS. 143 



Second phalanx of third digit, length .013 



Third phalanx of third digit, length .017 



Third phalanx of third digit, width of proximal end .009 



The Hind Limb presents fewer peculiarities than the fore limb, and, except in a 

 few details, is very similar to that of Eporeodon. The pelvis (PI. VI, Pigs. 46, 47) 

 is very like that of the Oregon form but with some minor differences. The ilium has 

 a shorter peduncle which expands more abruptly into a wider plate. The latter is 

 less strongly everted, especially at the antero-inferior angle, which is less prolonged. 

 The iliac surface is broader and more rounded, the acetabular border less prominent, 

 and the pubic border more so. The pit for the rectus femoris muscle is larger but 

 not so deep. The acetabulum is much larger and relatively shallower and the artic- 

 ular surface is more reduced by the very large sulcus for the round ligament. The 

 ischium is more twisted upon itself, so that the posterior end is much more everted 

 and depressed. The crest above the acetabulum descends more abruptly in front and 

 dies away behind without forming an ischiadic notch. The pubis in its free portion 

 is short and stout and the symphysis, in which the ischium shares, is elongate. 



The femur shows analogous differences from that of Eporeodon. The head is 

 distinctly larger and more sessile and has an unusually anterior position ; it does not 

 rise so far above the bridge connecting it with the great trochanter. This bridge is 

 more thickened in the antero-posterior dimension and the great trochanter is larger 

 and more massive. The shaft is heavier and more arched forward and, distally, is 

 both broader and deeper. The external linea aspera appears to be less conspicu- 

 ously marked and the pit for the plantaris muscle shallower. The condyles have a 

 greater vertical diameter but do not present so strongly backward. The rotular troch- 

 lea is wider; its margins are of equal height and more compressed. 



The tibia is very much alike in the two genera. In Mesoreodon the external 

 surface for the femoral condyle is broader and the cnemial crest more massive and 

 rugose ; the shaft is slightly heavier and the distal end rather more expanded, both 

 transversely and from before backward. The grooves for the astragalus are wider 

 and the intercondylar ridge broader and lower and not forming, as in Merycliyus, a 

 posterior tongue. The sulcus which invades the external astragalar groove is larger 

 and deeper, and the external groove is a little wider relatively to the internal than in 

 Eporeodon. An important change which is already indicated in the Oregon genus 

 is carried farther in Mesoreodon, viz., the presence of a distal facet for the fibula, 

 showing that the latter has extended slightly beneath the tibia. I cannot ascertain 

 the condition of the older species of Merycliyus in this respect, but in a specimen 

 belonging probably to M. elegans, from the upper Loup Fork, there is no fibular facet 



A. p. s. — VOL. xviii. s. 



