OF THE MESOZOIC MAMMALIA. 247 
Sertiol''’'’ condilioM, ullimatel; re™ll either in snppreerion or 
Photodonta. 
Dromotheriidie. 
Dromotherium. 
Microconodon. 
Phodidelpiiia. 
1 . Triconodoniidie. 
a. Amphilestes. 
Aniphitylus. 
Triconodon. 
Priacodon.* 
b. Pliascolotherium. 
Tiiiodoii. 
c. Spalacotherium. 
Menacodon.* 
2 . Amphitheriidte. 
Amphltherium. 
Diplocynodon. 
Docodon.* 
Enneodon. 
Perainui-. 
3. Peralestidar. 
Peralestes. 
Peraspalax. 
Paurodon. 
4. Kurtodrmlidx. 
Kurtodon. 
I.NSECTIVORA PkIMITIVA. 
5. Amblolheriidic. 
Amblotherium. 
Achyrodon. 
C. Stylacodmitidn-. 
Stylacodon. 
Laodon. 
Plia^colestes. 
Drvolfstes. 
Astlienodon. 
7. Leptocljjdus. 
From this table it is seen that the prevailing or typical dental formula in these 
mammals is i c x, p t, ni s- The incisors in no case exceed four. The premolars in 
the large majority of genera are either four or have recently been reduced to three ; 
in two cases in which the determination of the teeth is somewhat uncertain, five pre- 
molars have been observed ; the only other exceptions are in the Dromotheriidce, in 
which the premolars number three only. The molars are less constant, varying from, 
8-7 in all the more ancient genera to 4-3 in some of the more recent. 
The mode of reduction is by no means uniform in the different families but 
varies little within the limits of the families themselves and certainly tends to 
strengthen rather than, impair the family boundaries adopted in this memoir. 
In the T)'iconodo.ntid(e there are four incisors in the earlier genera which are 
reduced to three in the later forms, probably by the loss of The reduction of the 
premolar series seems to have been at the expense of for this is the smallest tootli 
Mandibular Dentition. 
Total 
-j 
i. 
c. 
p- 
m. 
p.&m 
Dentition 
Estimated 
1 Reduction &c. of Dental Series. 
3 
1 
3 
7 
56 
?3 
?7 
4 
1 
4 
7 
64 
4 
1 
4 
7 
64 
3 
4 
1 
1 
1 
4 
?3 
4-3 
4-8 
7 
48 
i 4 suppressed. 104 retarded or suppressed. 
Pi suppressed “ “ “ 
premolar series extremely reduced or suppressed. 
1 
?8 
?3 
. 
■ 
56 
reduced. 
?3 
i 4 suppressed. 
Pi suppressed. 
?4 
4 
6 
60 
3 
3 
1 
4 
8 
64 
P 2 atrophied, atrophied. 
3 
6 
60 
‘ “ m, suppressed. 
9 
52 
Pa suppressed, ni ,_8 suppressed. 
1 
4-5 
6 
1 
4 
7 
1 
2 
5 
Pi - 3 suppressed, suppressed? 
?1 
4 
‘ 
Pi_s atrophied, P 4 hypertrophied. 
4 
1 
4 
4 
7 
8 
64 
Pi atrophied, P 4 hypertrophied, m, atrophied. 
P 3-4 
4 
1 
1 
4 
?5 
7-8 
8 
68 
m, atrophied. 
4 
4 
1 
1 
4 
4 
8 
8 
68 
68 
Pi atrophied, m, atrophied. 
4 
1 
3 
8 
64 
Pi suppressed, “ “ 
4 
6 
_ 1 
