1857.] OWEN DICHODON CUSPIDATUS. 193 



aft extent, of crown of 7 lines, but is not thicker than 2 lines ; it has 

 been worn down almost to the roots, which are two in number ; the 

 groove between the ridge along the inner side of the base and the rest 

 of the crown remains : the smooth abraded horizontal surface, a line 

 or more in breadth, slopes away from the produced mid-part of the 

 crown, the general shape of which evidently corresponded with that 

 of the first deciduous molar of the lower jaw (op. cit. pi. 4. fig. 2,^ 1). 



The second premolar, fig. 4, p 2, with a fore-and-aft extent of 

 8 lines, is 3 lines thick : the smooth abraded surface slopes away from 

 the most prominent middle lobe of the crown, but rises so as to indi- 

 cate the summit of a fore and a hind accessory lobe : the groove 

 bounded by the inner basal ridge remains. This tooth has two fangs, 

 the hinder one being the strongest, where the crown is thickest. 



The third premolar, figs. 4 & 4 «, j? 3, has been displaced, but 

 lies attached to the matrix not far from its socket. Its crown is less 

 worn than that of the preceding tooth, and the trilobed character is 

 consequently better shown : its fore-and-aft extent is 8 lines, the same 

 almost as that of the deciduous tooth {loc. cit. fig. 2, p 3) which 

 preceded it ; but the three principal lobes are thickerj and the acces- 

 sory inner lobe, marked i in fig. 3, p 3, loc. cit., of the deciduous 

 tooth is more developed, the greatest thickness of the crown being 

 4 lines in the present premolar : the accessory tubercle at the back 

 part of the outer side of the crown is better developed. The inner 

 basal ridge continued from each end of the base of the inner tubercle, 

 i, is well marked. The line of abrasion which follows the undulations 

 of the tricuspid outer and inner part of the crown diminishes in 

 breadth from the fore to the back part of the crown. The height of 

 the middle lobe of the crown is not more than 3 lines. The thick 

 hinder root is longitudinally grooved, as if preparatory for the 

 bifurcation which the same root would probably present in the next 

 tooth. Unfortunately no other tooth is preserved in this specimen, 

 and the form and proportions of the fourth premolar of the upper 

 jaw have still to be determined. 



Sufficient, however, of the characters of the premolar series of the 

 adult Dichodon are now known to confirm the deductions from the 

 first-described evidences as to its generic distinction from DichobunCy 

 Cuv. : the imusual antero-posterior extent of the low crowns of the 

 first three premolars establishes that distinction, if even the fourth 

 premolar should prove, as is most probable, to have a form and pro- 

 portions more resembling those of the first true molar tooth. The 

 precise form and proportions of the last true molar of the lower 

 jaw, exhibited in Dr. Wright's specimen, aiford likewise a valuable 

 accession to the characters of this interesting Anoplotherioid extinct 

 British quadruped. 



The collection of the Marchioness of Hastings, now in the British 

 Museum, also includes a portion of the right ramus of the lower jaw, 

 with the last molar tooth. This tooth, fig. 5, corresponds in size and 

 shape with that in Dr. Wright's specimen, but it is more worn, having 

 belonged to a more aged animal. The two enamel-bounded crescents 

 of the anterior division of the crown have been ground down into a 



