1012 The American Naturalist. [December, 
There is another line of perissodactyls in which the meta- 
cone is flattened but not elongated, and no complete ectoloph 
is formed. I refer to the little Wasatch genus Heptodon (which 
Cope has erroneously placed in the ancestry of Hyrachyus), 
also Helaletes of the Bridger, an undoubted successor of Hepto- 
don, which Marsh was wrongly led to consider an ancestor of 
the Tapirs. The molars, studied by our six differentia, are 
found to differ from those of the rhinocerotine Hyrachyus by 
the incomplete ectoloph, also by the shifting inwards of the 
metacone and consequent shortening of the metaloph. - In 
looking about for molars with similar differentia, we find 
those of the true Lophiodon of Europe, L. isselense, for example, 
stand nearest. 
Now, how shall we distinguish the early Tapirs? First, 
there is no mesostyle ; second, the paracone and metacone (as 
observed by Cope) are both conic and symmetrical ; third, a 
feature of great importance, apparently unnoticed hitherto, is 
that the protoloph and metaloph spring from the anterior 
bases of the paracone and metacone, and not from near the 
apices of these external cusps as in all molars of rhinocerotine 
affinity. We find, as a general law, that where the external 
cusps are symmetrical as in Paleotheres, Horses and Tapirs, 
the transverse crests always arise in front; where they tend to 
asymmetry as in Helaletes, Lophiodon and Rhinoceros, the 
crests tend to rise from or near the apices. ` 
Enough has been said to make clear the new method of pro- 
cedure in the analysis and discrimination of early ungulate 
molars. Let us apply this form of statement and description 
to the aberrant lower Wasatch genus Meniscotherium as a re- 
sumé: 
Upper Molars, buno-selenodont ; paracone, metacone and 
protoconule selenoid; metaconule reduced, lophoid, united 
with hypocone; a large parastyle and mesostyle. Lower 
Molars, seleno-lophodont; metaconid reduplicated by metasty- 
lid. We find that a similar analysis may be given of Chalico- 
therium, excepting only “ protoconule reduced.” It is thus 
suggested that Meniscotherivm may be related to Chalicother- 
ium. 
