562 PROF. OWEN ON PRORASTOMTTS SIRENOIDES. 



may have been the third of the series (PI. XXIX. fig. 1, <z 3). The 

 next (d 4) is chiefly represented by a root, obliquely directed, like 

 the one in front (a 3), with the external longitudinal indent narrower 

 and deeper, more distinctly indicative of two connate fangs, with 

 the base of the crown, to which a fragment of enamel adheres. 



The outer, enamelled side of the crown of the tooth (ib. ib., d 5) 

 has been pushed inward out of place ; it is 4 lines from before back- 

 ward, 2 lines in extreme vertical extent at the middle of the crown. 

 The anterior fang of this tooth is exposed for 8 lines of its length. 



The sixth tooth (first molar, ib. ib.,mi) has also the longitudinal 

 much exceeding the vertical diameter of the crown; and the 

 outer exposed side is divided by a widish median indent (ib. fig. 3, i ) 

 into an anterior ( a ) and posterior ( b ) lobe. The fore-and-aft dia- 

 meter of the crown is 6 lines, the vertical diameter is 2 lines. The 

 outer sides of the two lobes are bulging or convex both vertically and 

 lengthwise; the inner sides are narrower (a' &'). The grinding-sur- 

 face has been worn to a common field of dentine. Of this tooth two 

 distinct external fangs are exposed (PI. XXVIII. fig. 1, m 1, and 

 PI. XXIX. fig. 1, mi). The seventh tooth (second molar, on 2) 

 shows a similar configuration, with increase of size (PL XXIX. 

 figs. 1 and 2, w2&7). The fore-and-aft extent of the crown is 8 lines ; 

 but the vertical diameter is barely 3 lines. The, anterior lobe (a, a') 

 is worn to nearly the bottom of the transverse dividing valley ( * ) ; 

 a feeble angle of dentine marks the summit of a low buttress or 

 fold at the hind part of the front lobe, descending to the outer end 

 of the valley ( • ) ; the hind lobe ( 5 ) has its transverse ridge abraded 

 to near the base, but a thin line of enamel next the valley remains. 

 The hind surface of this lobe shows a ridge (g) descending from the 

 middle of the back part of the worn upper surface downward and 

 outward to near the base of the crown, with a slight curve ; it defines 

 a flat facet (a) on the outer half of the hind surface of the crown, the 

 ridge representing a portion of an interrupted " cingulum." 



The fore part of the crown of the eighth tooth (third molar, m 3, 

 fig. 3) shows a transverse ridge traversing the fore part of the base of 

 the front lobe. The fracture across the skull passes through the front 

 lobe of this tooth; part of the hind lobe remains on the hinder 

 moiety of the fossil skull, and shows the valley deeper, through less 

 amount of wear, than in the antecedent molar ; yet the dentine has 

 been exposed upon the hind lobe to a breadth of half a line. The 

 inner surface of the hind lobe has no basal ridge. The transverse 

 breadth of the crown of this molar is 8 lines, the fore-and-aft breadth 

 is 9 lines. The hind surface is imbedded in the matrix ; but the 

 character of this part of the molar is given by the antecedent tooth. 



The crowns of the fifth, sixth, and seventh of the molar series are 

 preserved in the left maxillary, progressively increasing in antero- 

 posterior extent of crown, and in a more definite external indent 

 marking its division into two lobes. The two outer fangs are distinct 

 on the sixth and seventh teeth ; and one of the inner diverging roots 

 is shown on the fractured surface of the eighth tooth (last molar) of 

 this side of the jaw. 



