296 PROFESSOR OWEN ON SOME SPECIES OF THE EXTINCT GENUS NESODON. 
The second molar (ib. d 2) has been markedly larger than the first, but is too muti- 
lated for description ; it was implanted by two fangs. 
The third molar (ib. d.), of still increasing size, and chiefly m antero-posterior 
extent, presents a long compressed crown, divided into two lobes, convex externally, 
by an oblique, unequal-sided longitudinal angular indentation : the inner side of the 
Wnder and larger lobe is penetrated by two folds, extending obliquely outwards and 
forwards, fig. 85 3. , . ^ u •*. 
The fourth molar (ib. d^), with a slight increase of antero-posterior extent, has its 
anterior lobe indented internally. 
The crown of the fifth molar (ib. m i) resembles that of the fourth in configuration 
and size, but is narrower, from having been less worn. The grinders are placed close 
too-ether one behind another, in a straight line and a little overlapping. 
All the teeth present a deep brown, in some parts almost black, colour, with a 
polished shining surface. The enamel is remarkably thin, and is closely blended with 
the dentine which renders it very difficult to determine its extent upon the exterior 
of the crown: it appears to be continued much further upon the outer than the inner 
side of the tooth. _ • j ^.u * 
The incisors and canines being indicated by their position, there remained then to 
determine the nature of the five grinding teeth in place, on each side of both jaws. 
That this was not the entire number characterising the dental formula of the animal, 
was shown by the germ of a molar (Plate XVI. fig. 5, m .) in the fraetured hinder 
protuberance of the maxillary, behind the last grinder in place, the crown of which 
(ib. m 1) had very recently emerged from the socket. 
To obtain further insight into that formula— so important in the elucidation of the 
true generic character and affinities of the Nesodon—l removed the inner parietes of 
the sockets of the molars in the right ramus of the lower jaw, and, excavating below 
the base of the coronoid process, exposed there the germ of a molar (ib. fig. 7 , m2) 
answering to that forming the sixth (m2, fig. 5) in the upper jaw. The third {ds) 
and fourth (^^4) grinders were implanted by two long tapering and diverging fangs; 
but the fifth grinder (m 1) presented a marked difference ; its crown being continued 
undivided, with a slight and gradual diminution in antero-posterior extent, and 
corresponding increase in transverse thickness, to a level, half an inch lower 111 the 
deepening ramus of the jaw, than that of the end of the fangs of the antecedent grinder, 
d 4. The middle indentation on the inner side of the crown of the fifth grinder (m d 
gradually terminates 9 lines below the summit, the rest ot the inner side of the 
crown being almost flat: at its base a wide pulp-cavity is exposed (fig. 9, m 1), into 
which the obtuse conical end of a deeply inflected enamel-fold projects from above, 
indicating great variety in the pattern of the grinding surface at different stages of 
abrasion of the crown. 
From the difference between the fourth (d 4) and fifth (m 1) grinders, I conclude 
them to belong to different series of those teeth ; and, from the analogy of the tunes 
