SUCCESSION OF THE TEETH IN THE DASYURID/E. 
457 
changes that have taken place from the earliest Prototherian form (I.) down to such a 
fully developed Diphyodont dentition as is now possessed by Tapirus (IX.), from 
which again, or more directly from VIII., there have arisen, by the different processes 
of tooth variation, all the numerous forms of modern Eutherian dentition as exempli¬ 
fied on the diagram by X. ( Elephas),* XI. ( Hydromys ), XII. ( Felis ), or XIII. 
(Chiromys). t 
Again, working in another direction, we can obtain an idea of the tooth evolution 
that has taken place in the Marsupials by starting from the “ generalised Marsupial ” 
Fig. 4. 
Stage. 
Dentition. 
Process. Bemarks or examples. 
1 
c 
PM 
M 
( 
1 
2 
3 4 
“X 
5 
1 
1 
2 
3 
4 ' 
r~ 
1 
2 
3 
4 
5 
IV. 
V V 
V v V 
V 
V 
V 
V 
V 
IP 
1_1 
LJ 
LJ 
LJ 
O 
Generalised Mar¬ 
supial. 
IVo. 
V 
V 
V V V 
V 
V 
o 
V 
V 
IP 
LJ 
LJ 
LJ 
LJ 
O 
Loss of pm' 3 . 
Didelphys and most 
Perameles. 
IV6. 
V 
V 
V V 
o 
V 
V 
0 
V 
V 
IP 
1_1 
LJ 
LJ 
LJ 
O 
Loss of i 5 . 
Pliascologale, 
Thylacinus, and 
some Perameles. 
IVc. 
V 
V 
V V 
o 
V 
V 
0 
V 
V 
0 
LJ 
LJ 
LJ 
LJ 
L 
Loss of milk pm 4 
and retention of 
m 5 . 
Myrmecobius. 
IV d. 
V 
V 
V V 
o 
V 
V 
o 
V 
0 
LJ 
LJ 
LJ 
LJ 
0 
Loss of pm 4 . 
Dasyurus. 
IVe. 
V V 
V o 
o 
V 
V 
o 
V 
V 
IP 
LJ 
LJ 
LJ 
LJ 
0 
Loss of i 4 from IV6. 
Pseudochirus, 
Thylacoleo, &c. 
iv/. 
V V 
V o 
o 
V 
■* 
o 
o 
o 
V 
w 
LJ 
LJ 
LJ 
LI 
0 
Loss of pms 1 and 3 . 
Keduction in size 
of milk pm 4 . 
Phascolarctos. 
IV;/. 
V 
o 
0 o 
o 
o 
o 
o 
o 
V 
LJ 
LJ 
LJ 
LJ 
0 
Loss of i 3 aud 3 , 
canine and milk 
Pliascolomys. 
pm 4 , from IV/. 
IV h. 
v v 
V o 
0 
o 
o 
o 
V 
V 
LJ 
LJ 
LJ 
LJ 
0 
Loss of canine and 
pm 1 from IVcZ. 
Macropus.X 
stage represented by IV. in figs. 1 and 2, at which point the direct evolution of 
Diphyodontism was in their case arrested, and drawing up a similar diagram (fig. 4) to 
those already given. This diagram, however, is quite simple, and only depends on the 
loss or variation of individual teeth, and therefore does not need any detailed expla¬ 
nation beyond what is placed under the headings of “ Process ” and “ Remarks ” in 
the diagram itself. The position of this line of dental evolution in the general system 
is shown on Plate 2 under the heading of “ Metatherian branch.” 
* No evidence as yet exists as to which of the three incisors is represented by the Elephant’s tusk, 
which is here only provisionally called i 1 . 
f See Petees, ‘Berlin, Akad. Abhandl.,’ 1865 ( Pkys .), p. 79 et seq., PI. 2. 
J Of course it is not pretended that the dentitions of these animals are directly descended from one 
another, hut the diagram serves to show by what steps any individual dentition may have been evolved 
from the generalised type. 
MDCCCLXXX VII.—B. 
o N 
