80 



In the Uiird premular the inner lobe is less well developed at its fore part 

 than in the fotirth. 



The crown of the second premolar (Figs. 19, 22) is formed of a single 

 conical lobe, corresponding with the external lobe of the succeeding tooth. 

 Postero-internally, it presents a feeble rudiment of an inner lobe. The 

 crowns of the premolars were worn away mostly in a slanting manner poste- 

 riorly. The exposed dentine in the two lobed crowns became continuous at 

 ». the back of the crown. 



The molars above described resemble, in construction and in the relative 

 position of the six lobes of the crown, those of Hyracotherium and Pliolophus, 

 two extinct genera of pachyderms, described by Professor Owen from remains 

 found in the London clay, an Eocene formation of the estuary of the Thames. 

 In both the genera named the last molar is ])roportionately better developed ; 

 and in all the molars the postero-internal lobe and the basal ridge are likewise 

 proportionately better developed. The upper pi-emolars are quite different.. 

 In Hyracotherium the back t\yo premolars have five lobed crowns, and in 

 Pliolophus the last premolar has a similar constitution. 



Too small a portion of the jaw (Fig. 18) containing the teeth above 

 described has been preserved to ascertain anything of importance as to the 

 shape of the face. The infra-orbital foramen is situated immediately above 

 the interval of the back two premolars. 



Measurements from some of the upper-jaw specimens and teeth above 

 described are as follows : 



Specimens in Plato VI. 



Figs. 18,19. 



i Lines. 



Si)ace occupied by series of six molar teetb 9 



Space occupied liy true molars 5 J 



Space occupied by tbree premolars 3^ 



Breadtb of .second premolar 1 



Widtb of second premolar 1 



lireadtli of tbird premolar ' IJ 



Width of tbird premolar li 



Breadtb of fourth premolar i 1^ 



Width of fourth premolar 2 



Breadth of first molar '' 1^ 



Width of first molar ' 2^ 



Breadtb of second molar i 2 



Widtb of secoud molar 2J 



Breadth of last molar 1^ 



Width of last molar 2 



Fig. 20. 



21 



U 

 2i 



^ 



21 



12 



2i 



