794 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
part of the base of the front lobe, rapidly rises as it curves inward, and extends as 
a thick ridge three lines in advance of the front lobe, rising nearly to its level, and 
assuming more of the character of an accessory lobe than a mere basal ridge or deve- 
loped portion of the “ cingulum.” Its lobular appearance is strengthened by the well- 
developed link (s) which connects its outer angle with the fore part of the front lobe 
(a) near its swollen end. The accessory ridge (n), internal to the link, is well marked, 
but subsides before reaching the prebasal ridge. This sinks more gradually and with 
less loss of thickness to the inner and fore part of the base of the front lobe than at its 
outer end or beginning. The anterior surface of this lobe is broken by minor and less 
regular ridges and grooves of enamel. The mid link ( r ) has the same relative position 
to the transverse eminences it connects as has the fore link ; the inner accessory ridge 
(o) subsides in the valley ; smaller subsidiary ridges and grooves accentuate and multiply 
the hard enamel-constituent of the grinding-surface of the lower molars, as in those of 
the upper jaw. 
The last molar (m 3), with a very slight decrease of breadth of the hind lobe, repeats 
the characters of the preceding tooth ; in both, the hind surface (Plate LXXIX. fig. 10) 
is impressed with a pair of narrow conical excavations, with apices not reaching to the 
basal beginning of the crown ; these impressions define or leave three ridges (A), not 
extending back beyond the smooth basal part of the tooth, but which, when worn down 
to near that part, give a strongly undulating course to the enamelled summit of the hind 
lobe of the molar. 
The most complete example of a lower jaw of Procoptodon is that which was pre- 
sented to the Museum of the Royal College of Surgeons of England in the year 1853, 
by Dr. F alder, with a note of its discovery in the freshwater or drift beds of Darling 
Downs, Queensland, “ at a depth of 40 feet from the surface of the soil.” 
Each ramus of the jaw is preserved as far as the beginning of the horizontal branch ; 
a small portion of the alveoli of the two incisors, with the corresponding part of the 
diastemal ridges, has been broken away ; the lower border of the right ramus has like- 
wise suffered. But the most instructive element in the jaw, viz. the molar series, is 
almost entire in both rami. 
This series includes six teeth. The last molar is represented by a partially developed 
crown in its formative cell ; the next in advance is not fully risen into place, and the 
summits of its two lobes are unworn. The antepenultimate molar, with these ridges 
just touched, shows on each a polished linear tract of enamel ; the three anterior teeth, 
with progressively increasing degrees of wear and decrease of size as they precede in 
position, are therefore deciduous molars. Of this phase of dentition, as seen from 
the outer side view of the right ramus, a figure is given in Plate LXXX. fig. 6. 
The foremost tooth (d 2 ) shows a working-surface of a triangular form, the base turned 
backward, the apex forward and obtuse. The outer border has a submedian notch 
corresponding to a groove terminating there, which divides the outer surface into a fore 
and hind lobe, both of which are convex transversely, and in a minor degree vertically. 
