BLAKE — ON DIDTMODON YAUCLUSIANUM. 
9 
sures 27mm. ; its greatest vertical depth between the penultimate 
and last molar being 11mm. 
The last molar {on 3) measures 7mm. in length, and 4 in breadth. 
Its form is quadricuspid ; the two outward cusps being least eroded ; 
from the ectoposterior cusp is developed a slight basal talon, ex- 
tending towards the entoposterior cusp, which is the smallest of the 
four, pyramidal, and acuminate ; the entoanterior cusp is larger, and 
is tipped with a small exposed ring of enamel ; the ectoanterior cusp 
is much worn ; there is no trace of the distinct hinder lobe of Xipho- 
doD, which lobe in the Dichobune (sp. ?) from Hordwell, marked 
29714 § in the British Museum, exhibits a well-marked bicuspid divi- 
sion, having the eflfect of rendering the ultimate molar in that speci- 
men virtually hexacuspid, to a greater extent than in the Dichobune 
ovina. 
The second molar, 7mm. in length and 4 in breadth, has also four 
cusps; the ectoposterior one being the most worn, and liaving a dis- 
tinct basal posterior talon running from it to the foot of the ento- 
posterior cusp ; the two anterior cusps are much the highest, a sabre- 
shaped band of enamel running from the base of the ectoanterior 
cusp nearly to the summit of the entoanterior cusp. 
The fractured first molar has the posterior half broken away be- 
neath the maxillary alveoli ; it exhibits the traces of a distinct iang ; 
its anterior portion shows an eroded surface, affording a slight re- 
semblance to the bicrescentic contour of the same part in Dicliobune, 
I have compared this fossil with tiie specimens, figures, and de- 
scriptions accessible to me of Dichobune, Xiphodon, Cainothcrium, 
Hyfggulus, Ampliitragulus, Tapirulus, Aphelotherium, Dichodon, 
Heterohyus, Acotherulum. Of tlie latter genus, which closely ap- 
proached Didymodon, Gervais remarks as follows: — ^''Th.e Acotherulum 
saturninum appears to be related to the Dichobuues ; but its hinder 
molars have only 2 tubercles on each ridge, and in this relation it has 
most analogy with Paheochicrus and Choeromorus, for Dichobune 
has 3 tubercles on the anterior ridge." Gervais figures, on his 24tli 
plate, the 4 antepenultimate superior molars, and 3 inferior molars of 
the left side. These were obtained from the lignites of Debruge, 
near Apt. The lower teeth differ from Didymodon, should my inter- 
pretation of their homologies prove correct, by having a distinct 
quinquecuspid pattern to the 2nd molar, whilst the 3rd molar exhi- 
bits (so far as the fractured tooth, half of which is broken away, can 
yield any decided information) no trace of the well-defined dichoto- 
moua division of its posterior portion in the new form. 
In Heterohyus armatus the last molar is " tuberculeuse, tres-emous- 
see, simulant en avant une fausse coUine transverse un peu oblique" 
(Gervais, pi. xxxv. p. 7), the difference existing between the pe- 
nultimate and antepenultimate molars of the two forms precluding 
* This specimen (No. 29714) consists of the last and half the penultimate molars of 
a Dichobune ; the former measuring 14 mm. in length and 8 mm. in breadth. In the 
specimen marked 29856 the cusps on the posterior lobe are worn, the brcjldth as weU 
as the length of the teeth being much smaller than in 29714. 
VOL. VI. C 
