BLA.KE — ON DIDYMODON VAUCLUSIANUM. 



9 



sures 27mm. ; its greatest vertical depth between the penultimate 

 and last molar being 11mm. 



The last molar (m 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- 

 don, which lobe in the Dichobune (sp. ?) from Hordwell, marked 

 29714 § in the British Museum, exhibits a well-marked bicuspid divi- 

 sion, having the effect 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 having 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 fang ; 

 its anterior portion shows an eroded surface, affording a slight re- 

 semblance to the bicrescentic contour of the same part in Dichobune. 



I have compared this fossil with the specimens, figures, and de- 

 scriptions accessible to me of Dichobune, Xiphodon, Cainotherium, 

 Hysegulus, Amphitragulus, Tapirulus, Aphelotherium, Dichodon, 

 Heterohyus, Acotherulum. Of the latter genus, which closely ap- 

 proached Didymodon, Gervais remarks as follows: — "The Acotherulum 

 sulurninum appears to be related to the Dichobunes ; but its hinder 

 paolars have only 2 tubercles on each ridge, and in this relation it has 

 most analogy with Palaeocha3rus and Chceromorus, for Dichobune 

 has 3 tubercles on the anterior ridge." Gervais figures, on his 24th 

 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- 

 mous division of its posterior portion in the new form. 



In ILctcrohyus armatus the last molar is " tuberculeuse, tres-emous- 

 see, simulant en avant une fausse colline 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. iu Length anil 8 mm. in breadth. Iu the 

 specimen marked 2 l JS56 the cusps on the posterior lobe arc worn, the breadth as well 

 as the length of the teeth being much smaller than in 29714. 



VOL. VI. C 



