68 Dr. B. Petronievics on the 



hesitated to affirm it categorically. The shaded part below 

 indicates the lower surface of the jaw, which was already 

 uncovered before the new preparation. 



PI. III. fig. 2 shows the newly prepared inner side of the 

 fragment, which sets beyond any doubt that this fragment is 

 a lower jaw. Its lower edge is wholly uncovered in the 

 front part, whilst a narrow band of bone remained covered 



behind. The line shows the position of the lower edge 



in this hind part in concordance with the lower edge in fig. 1. 

 A faint groove seems to occur in the front part, possibly a 

 trace of the mylohyoid groove. 



PI. III. fig. 3 shows the upper surface of the three molar 

 teeih. It is probable that in front of them there were three 

 more teeth. As the hindmost molar (w 3 ) seems to be some- 

 what smaller than the middle one, so it is probable that it 

 represents the last molar of the jaw. The valleys between 

 the obliquely placed cones are especially marked in this figure. 

 The grooves between the middle and inner cones of m 2 and v> 3 , 

 which are interrupted only where the edges of the oblique 

 valleys meet one another, are marked in the figure as empty 

 space.*. These grooves are clearly distinct from the oblique 

 valleys between the cusps, but narrow in comparison with 

 the cusps. 



To the detailed description of the middle tooth by Owen 

 (1857) I must add some corrections. Our fig. 5 (PI. III.) 

 shows, when compared with fig. 3 of Owen, that there is no 

 such prominent basal cusp on the outer side of this tooth 

 as is marked in Owen's figure*, and our fig. 6 shows, com- 

 pared with Owen's fig. 4, that its inner cones are not " slightly 

 inclined forwards" (comp. Owen, 1857, p. 2), as it is quite 

 wrongly indicated by this last figure of Owen. Fig. 7 shows 

 the two middle cusps of this tooth seen from the inner side 

 that have not been figured by Owen. The oblique position 

 of the cusps is quite clearly indicated in this figure. In 

 figs. 5 and 6 the cement that coats the roots is shaded. 



I conclude this paper with a remark concerning the 

 probable direction of the motion of lower jaw in IStereo- 

 gnathus. According to the mechanical theory of teeth-forms 

 proposed by Ryder and Cope, the oblique position of the 

 molars in some rodents (upwards and forwards for the lower 

 and downwards and backwards for the upper molars) is due to 



* Unfortunately the hinder cusp of this tooth, shown so conspicuously 

 in fig, o of Owen, has been broken awaj Bince Owen's time. 



