747 
and metacone are more important cusps than the protocone. So far 
as the fossil Primates of the lower eocene are known we find the 
protoconid is the most prominent cusp in the lower molars while in 
the upper molars the protocone is less prominent than the external 
cusps. RösE’s argument really turns therefore upon the expectation that 
foetal development should repeat ancestral history of the cretaceous 
period! As the flattened form of the crown is from the start a cainozoic 
type, we should hardly expect the order of cusp succession to invariably 
revert to a mesozoic type. While not thoroughly convincing, there is 
a great deal of force in this way of meeting the embryological data. 
Nomenclature. Röse (p. 400) apparently mistakes the homo- 
logies of the lower molar cusps of man for he has overlooked the 
fact that the primitive anterior lingual cusp, or paraconid, has degen- 
erated in the Primates (excepting in a few Lemurs) while it persists 
in Didelphys. It is not seen in the human lower molar at all. 
Its declining stages mark the loss of sectorial function and can be 
readily followed in the lemurs, and fossil monkeys; as shown by 
Corr and myself it degenerates while the hypocone in the upper molars 
develops. It follows that the anterior lingual in man is the meta- 
conid, while in Didelphys it is the paraconid and the mid-lingual 
is the metaconid. The posterior lateral cusp is undoubtedly the hypo- 
conid. RÖSsE proposes the term “pentaconid” for the distal or poste- 
rior intermediate cusp (ms¢, Fig. 1, 8). The term is inappropriate 
because this is not the fifth but the sixth cusp when we reckon the 
paraconid. It is analogous to the intermediate tubercles of the upper 
molars I have therefore suggested the term “hypoconulid” for it; this 
cusp is almost universal among lower eocene Mammalia; in the last 
lower molar it forms the additional lobe; it is found strongly devel- 
oped in many of the higher Primates. 
R6sE (p. 406) expresses the belief that the typical form of pri- 
mate molar was quadritubercular as opposed to Copr’s view that tri- 
tuberculy in human dentition is a reversion to the Lemurine type. The 
study of the fossil forms as well as of any complete zoölogical series 
can leave no doubt that the quadritubercular form is a comparatively 
recent acquisition. 
. In conclasion I would refer both these authors to the types of 
molar teeth found among the mesozoic Mammalia. It was while 
studying the rich collection in the British Museum that I became 
convinced of the force and universal application of the tritubercular 
theory proposed by Cop. 
American Museum of Natural History, 
New York, July 18th 1892. 
