No. 377-] THE ORIGIN OF THE MAMMALIA. 331 
General Conclusions. 
It is obvious that we must await a more complete knowledge 
of the skeleton of these various forms before we can confidently 
either classify them or establish their relations to Mammalia. 
The literature is in considerable confusion, and requires a more 
careful and exhaustive revision than I have been able to give it. 
It appears that the mammalian resemblances of these animals 
include a very large number of characters which are observed 
without exception in the basal Eocene or Puerco fauna of North 
America. 
The anticipation of the triconodont and multituberculate 
type of dentition of the Jurassic périod is remarkable. If 
actually phyletic, it points to an extremely early divergence of 
these-dental types— much earlier than the period of the 
Protodonta. 
The general resemblances with existing and basal Eocene 
types of mammals may be summed up as follows: 
Theriodont Characters. 
1. Teeth heterodont, four series; 
molars single rooted or with grooved 
fangs of triconodont and multituber- 
cular type. 
2. Anterior nares terminal. Pos- 
terior nares placed far back and | 
roofed over by palatines and maxil- 
aries. : 
3. Nasals narrow anteriorly, ex- 
panding posteriorly. 
4. Separate prefrontals; sepa- 
rate postorbitals closing orbits pos- 
teriorly. 
5. A single infratemporal or zyg- 
omatic arch consisting of malars and 
Squamosals (or consisting of fusion 
of upper with lower arches, Baur, 
Case). 
6. Quadrate reduced and over- 
lapped by squamosal. 
Promammalian Characters. 
Same characters observed in 
eR sO Multituberculata, and 
Triconodonta, except that the latter 
have completely paired molar fangs. 
2. The same in basal Eocene 
mammals, 
3. The same in basal Eocene 
mammals. 
4. Noprefrontals or postorbitals. 
Orbits open posteriorly in all bas al 
Eocene mammals. 
5. An infratemporal or zygo- 
matic arch only 
6. Quadrate probably coalesced 
with squamosal, occasionally sepa- 
rated by reversion (Albrecht). 
