SKCON'l) OUTLIXK OF TRITUBERCULY 87 



as in Palreotheres, 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 procedure 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 resume : 



Upper Molars, buno-seleiiodont ; paracone, metacone and protoconule 

 selenoid ; metaconule reduced, lophoid, united with hypocone ; a large 

 parastyle and mesostyle. Lower Molars, seleno-lophodont ; metaconid re- 

 duplicated by metastylid. We h'nd that a similar analysis may be given 

 of Chalicotherium, excepting only " protoconule reduced." It is thus 

 suggested that Me.n.ixcnfJt<'ri//in may be related to Chalicotherium* 



This method may be summarized as follows : Look for traces of 

 />////> i fire ancestral structure in the form and position of the cusps. 

 Second, determine the divergent form, position, proportions and relations 

 of the cusps. Third, determine the secondary cusps, crests and foldings, 

 their form and relations. Finally, let us turn to a wholly different molar 

 type and examine the complex and aberrant molars of Cori/pJwdon. Can 

 we establish any homologies between its elements and those of any of the 

 ungulates we have been considering ? Fortunately we are partly guided by 

 the molar of the Puerco genus Pantolambda Cope, which is even older than 

 the Coryphodons. This is our key to the ancestral or primitive form, and 

 by its aid Cope has, we think, rightly interpreted the homologies of the 

 Coryphodon molar elements. We first note that nature has here evolved 

 a lophodout crown from the tritubercular or trigonal basis, for there is no 

 distinct talon or hypocone except in the unique form Manteodon. 

 Pantolambda has no parastyle, t but a prominent mesostyle and a pair of 

 selenoid external cusps, also a seleuoid protocone with a spur leading 

 toward a protoconule and suggesting an incipient protoloph. The selenoid 

 external cusps of this type suggest a comparison with the lopho-selenodont 

 perissodactyls, and we are able to reach the following result. 



In a large series of Corijphodon molars we see first that the protoloph 

 is formed of the protocone, protoconule and parastyle, exactly as in the 

 horses. Unlike the horse (Anchitherium), the ectoloph is more or less 

 detached from the protoloph, but the examination of a large series of 

 specimens in the American Museum and Cope's collection convince us that 

 it is composed of the same elements as in AnrJi/fJ/erium, namely, the 

 paracone, which has almost lost its crescentic form, the mesostyle, which 

 is much less prominent, and the metacone, which is still crescentic. This 



* [See however p. 184, where Chalicotherium is held to be more probably au aberrant 

 Perissodactyl. ED. ] 



t [This is obviously a lapxus calami, the parastyle being especially prominent. See 

 Fig. 140. -ED.] 



