262 COPE: (Vor. HI. 
a way which unmistakably shows the gradual steps of the process, 
we may be excused for thinking the same to have been the case 
here, although without positive tangible evidence in the shape 
of intermediate fossil forms that exhibit such a passage from 
the ordinary type.” 
In 1882 I had the 
pleasure of discover- 
ing a genus! (Psitta- 
cotherium Cope), 
which supplies the 
desideratum wanting 
when Professor Ry- 
der wrote. This isa 
genus without dias- 
tema, and with two 
effective rodent-like 
Figure 84.— Psittacotherium multifragum Cope, incisors in each ra- 
left mandibular ramus; one-half nat. size; original; mus of the lower jaw. 
from Puerco bed of New Mexico. Fig. a, external Ectoganus Cope is 
5 
probably similar in 
these respects, but 
only its separate teeth 
have been found. 
Psittacotherium is 
then a_ generalized 
type and is not far 
from if not directly in 
the line of the ances- 
try of all Rodentia. 
It belongs to the Pu- 
erco fauna, which 
embraced so many of 
the progenitors of la- 
ter Mammalia (Fig. 
84). 
view; 2, superior view. 
Figure 85. — Calamodon simplex Cope, lowe jaw, I have called atten- 
left ramus; one-third nat. size; original; from Wasatch |. Raa h 
Eocene of Wyoming. Fig. @, external view; 4, supe- tion to the tact that 
rior; cd, inferior molar; ¢, exterior, d, posterior views. the first inferior inci- 
1 4merican Naturalist, February 1882. Tertiary Vertebrata, 1885, p. 195. 
