1892.] Zoology. 623 
or more commonly the protocone appears second, and the metacone 
third, then the protoconule appears, the hypocone, followed finally 
by the metaconule. Similarly the lower premolars do not repeat the 
ancestral lower molar history, the order is protoconid, hypoconid, 
metaconid, entoconid. “Scott! has worked this out in the Artiodactyla 
as follows: 4th. upper premolar—paracone (protocone), protocone 
deuterocone), metacone (tritocone), hypocone (tetartocone). 4th. lower 
premolar—protoconid, metaconid (deuteroconid), hypoconid, ento- 
conid.] Turning again to Laeker’s investigation we find that: 
5. In the lower jaw the fourth milk molar the order is protoconid, 
? paraconid, (anterior cusp) hypoconid, metaconid, entoconid. [The 
homology of the paraconid is somewhat uncertain. ] 
In considering the exceptions between ontogenesis and phylogenesis 
here noted, we must remember the extreme antiquity of some of these 
structures, dating back to the middle and lower Eocene, for upon the 
whole the parallelism is most striking —Hrnry F. Ossory, American 
Museum of Natural History, New York, May 23rd, 1892. 
1“ Osteology of Potbrotherium,” Journ. of Morphology, June 1891, pp. 48-49. 
