75 
is the first attempt after that of Winge to establish a complete 
theory of the mammalian tooth-phylogeny. Supported by Cope's 
investigations into the Puerco-fauna, he traced the pedigree of every 
tooth-cusp and formulated the following: I. The haplodont type. 
Crown simple and conical, fang simple, not distinguishable from 
the crown. This (reptilian) type has not as yet been discovered 
among the mammals, but leads through the protodont sub-type 
with lateral accessory cuspules and grooved fang (Dromatherium) 
to II the triconodont type with double fang and a distinct 
lateral cusp in front of (paracone, paraconid) and behind (metacone, 
metaconid) the central cone (protocone, protoconid), (Triconodon). 
III. Now a rotation of the lateral cusps takes place so that those 
in the upper teeth swing outwards, in the lower inwards; the grinding 
surfaces of the teeth form triangles which above turn an acute 
angle inwards and below outwards: tritubercular type (Spala- 
cotherium, Asthenodon, still to be seen in Chrysochloris, Centetes a. 0). 
From this point the evolution of the upper differs from that of the 
lower teeth. Behind the high primitive triangle of the lower teeth 
a low talonid first arises and on this two cusps are developed, 
hypoconid (on the outer side) and ”entoconid (on the inner side) 
and between them sometimes a third, hypoconulid, is added. — Be- 
hind the protocone (upper molars) a talon is evolved, generally 
with only one cusp, hypocone, and between proto- and paracone 
sometimes a cuspule may be developed, protoconulus, and similarly 
between the proto- and metacone a metaconulus. Thus we can have 
6-cuspid teeth above and below, but only the three cusps in the 
Primitive triangle are mutually homologous. — The bunodont 
4-cuspid tooth consists of proto-, para-, meta- and hypocone above, 
Proto-, meta-, hypo- and entoconid below, and so their cusps are 
not all homologous. Through decrease and increase of some of the 
Cusps, development of crests (lobes), cingulum and its styli, the 
different tooth-forms are produced; but invariably the protocone is 
the foremost inner, the protoconid the foremost outer cusp. 
In the following year Cope (in "The mechanical causes of the 
