198 
ON THE STKUCTUKE AND CLASSIFICATION 
is just appearing above the alveolar border. The third of the series, e, is still 
larger, T. ferox (PI. Ill, hg. 11), and we observe that is fully exposed and pn^ has 
come fully into position. The fourth of the series, d, is T. mordax (Willett) it is 
slightly smaller than the third, there are two premolars and four molars, fully exposed 
in place. At the time this .specimen was described by Mr. Willett \ Professor Flower 
suggested two hypotheses to account for the extra tooth of molar form : (1), That 
the most anterior of these teeth represented the single deciduous premolar, d^, 
which in the marsupials is molariform^; (2), That all the teeth preserved belong to 
the permanent set, when the dental formula will be pm 3 m 4, and indicate the 
most fully matured specimen as yet discovered. The writer adopts the second 
with the exception of the formula of T. mordax, which he 
believes to be pm 4 m 4, on the following grounds. It is 
evident that in Tricoiiodon, as in the recent marsupial 
Thylacinua^, the posterior molars are very late in coming 
into place ; the first molar, in the specimen under consid- 
eration, resembles the other molars much more closely 
eration, resemoies tne otner molars muen more closely 
anterior molariform tooth in T. serrula, and 
is therefore probably a true molar ; in all the specimens 
o of Triconodon thus far observed there are four premolars. 
The following hypothesis seems to conform to all the 
present evidence, viz.: the fully adult dental formula is 
p>m 4, m 4; the single deciduous tooth is the fourth pre- 
Kicii-RE3. A^erie8of Tricono- molar, d^, which is molariform ; the fourth molar is very 
don mandibles, all drawn natural late in Coming in. 
si*e, representing the (?rowth of the . j • rr, • , , 
mandible in relation to the succes- According to this the IViacantJiodon serrida, a, is an 
Sion of the teeth, a Triacanihodon immature THconodoii with the formula pm 3 d 1 m 4 the 
“ ::: The ?: s, 
dax.K somewhat older individual. older, the formula being pm 4 m 3 (;«4 still in 
d T. mordax (Mr. Willett’s type', its capsule). The T. ferox, c, is still older. The T. mor- 
probably a fully mature individual, f^^y mature with m , in place. 
1 Iterc is little- or no doubt that the most anterior tooth of molar form in 
T. sernda is the fourth deciduous premolar, but we must admit that the balance of 
evidence derived from the majority of specimens belonging to T. ferox and T. mordax 
ir. WilUtt, Etq. 
• ir. ir. Flmirr. 
** the Development and Succession of. the Teeth in the Marsupialia 
■ Flowr. 
t>p. cit., p. 6.39. 
