198 MR. OLDFIELD THOMAS ON THE [NoV. 15, 



meeting each other at a sharp angle, so that no part of the upper 

 tooth clears the face of the lower one. On the other hand, the 

 line of the teeth in Phacochcerihs is such as to carry the ends of 

 the upper pair quite clear of the lower ones. Now in Hylochcenis 

 we find an intermediate condition of set and curvature, and 

 consequently the upper teeth project a little beyond the ends of 

 the lower ones, without being so conspicuously developed as in 

 Phacochoerus. 



The lower canines are as widely splayed as in Phacochoerii^s, or 

 even slightly more so, the angle that the line of one makes with 

 that of the other, when viewed from the front, considerably 

 exceeding a right angle, this angle slightly exceeding a right 

 angle in Phacochcerus, and falling considerably short of one in all 

 other pigs. In section the lower canines are of the more primi- 

 tive shape found in the Sus verrricosus grovip, the outer face being 

 nearly equal to the inner, the hinder face being nearly transverse 

 and passing into the wearing surface without noticeable angle. 

 [In Potamoclio&rus and the Sus scrofa group the outer face is 

 much narrower than the inner one, and the posterior face is 

 directed obliquely outwards and is at a conspicuously different 

 angle to the surface worn against the upper canine.] Both oviter 

 and inner faces have a median longitudinal ridge, really slight but 

 appearing conspicuous owing to its being worn white as compared 

 with the general black colour of the tooth ; speaking strictly, 

 therefore, owing to these median ridges, the section of each canine 

 is not a triangle but a pentagon. 



The premolars appear at first sight to be three in number 

 above, as in ordinary swine, but closer examination shows the 

 remarkable fact that in both specimens the true last premolar (p^) 

 has been entirely suppressed, the tooth standing in its place 

 being — in the old as well as in the immature specimen — its milk- 

 predecessor (mp^). This latter tooth is very similar in shape to 

 the mp* of Phacochcerus, in which animal, however, the normal 

 tooth-change takes place. But in the lower jaw, curiously enough, 

 mp4 has fallen as is usual, and is replaced by p^. 



This suppression of p* is a most peculiar character, but occur- 

 ring in two specimens it does not seem permissible to suppose it 

 is only an abnormality, a point that in any case future material 

 will decide. Should it prove a normal character of the animal, 

 it would indicate that in this one respect Hylochcerus has gone 

 further in the suppression of its anterior cheek-teeth than even 

 Phacochcerus. 



Below (one specimen only) there is but one premolar present, 

 p^, an unusually simple tooth, without secondary cusps of any sort. 

 In front of it there are the roots of some additional premolars, 

 but it is not possible to say how many of them have ever been 

 developed, and for this we must await the advent of younger 

 specimens. 



The molars, above and below, are neither of the complicated 

 bunodont structure of those of Sus and Potamochcerus on the one 



