11 



NOTE ON THE UPPER INCISOR OF PHASCOLONUS. 



By C. W. De Vis, M.A., Core. Mem. 



(Plate I.) 



A lately acquired remnant of the upper jaw of a Phascolomis 

 gigas throws a welcome light on the nature of its incisor. The 

 fragment consists of the left premaxillary with a portion of the 

 nasal, and so much of the maxillary as includes the anterior wall 

 of the alveolus of the premolar. This socket has been occupied 

 by a curved columnar prismatic tooth, angular in front, such as is 

 exemplified by a loose {>reniolar of Phascolomis now in evidence, 

 and such as is required to fill an empty socket in another specimen. 

 On these grounds alone, apart from others to be adduced hereafter, 

 the derivation of the fossil from Phascolonus may be confidently 

 afiirmed. Included in it is the greater part of an incisor. At its 

 outlet, where its free portion has been broken away, its section is 

 an oval, constricted in the middle of its length, 42 mm. in its 

 vertical and 22 mm. in its transverse diameter ; measurements 

 which indicate an unexpected robustness of form. The lateral 

 constriction, increasing as it recedes, forms on the exposed surface 

 of the inner side of the tooth a broad deep groove, which, with a 

 similar channel on the opposite side, partially divides the fang 

 into two unequal columns, the lower of them being the larger. 

 The end of this lower one is broken away ; the smaller and upper 

 column rapidly contracts with a striated and puckered surface to 

 the edge of a funnel-shaped cavity, at the bottom of which is a 

 loop-shaped adit into the interior of the column. The ends of the 

 two columns were at some distance apart and not in the same 

 vertical line. 



It has tor some time been suspected by the writer that the 

 PJiascolonus incisor would prove to end in this manner ; it was an 

 opinion based on certain features in the alveoli of a maxillary 



