306 PROFESSOR OWEN ON SOME SPECIES OF THE EXTINCT GENUS NESODON. 
of enamel, into two almost consolidated fangs, the ends of which are broken off, 
showing in each the very contracted remnant of the pulp-canal. The enamel is 
continued 9 lines below the termination of the external groove, is continued a short 
way down each division of the root, and is characterized by four transverse rows of 
close-set small circular pits. The length of the enamelled crown is 1 inch 5 lines, its 
breadth 11 lines, its thickness 8 lines. The tooth above described is from the left 
side of the jaw ; its fellow from the right side is preserved, but in a more mutilated 
condition. 
A tooth, Plate XVII. fig. 17, which, in the unequal size of the two lobes of the 
crown, tallies with the third and fourth premolars of the Nesodon imhricatus, and, 
by its superior size to fig. 16, answers to the fourth premolar (p 4 ), has had the com- 
plexities of the grinding surface reduced by extensive attrition to the bottom of the 
deepest of the internal folds, a. It consequently resembles the foregoing tooth (fig. 16> 
except in its superior size, and in the greater extent of the hinder lobe, which is 
less convex externally. The outer plate of enamel, below the longitudinal indenta- 
tion, shows the same coarse and punctate transverse markings. The more regular 
and delicate striee of growth are beautifully and clearly shown. The posterior of 
the two roots, which is the largest, has a narrow central pulp-cavity. The external 
coat of cement is continued a little way upon the enamelled parts of the crown, and 
very plainly coats the anterior and posterior tracts where the enamel is interrupted. 
The length of the remainder of the enamelled crown of this tooth is 2 inches 
2 lines, its breadth 1 inch 1 line, its thickness 7 lines. 
A portion of tooth (Plate XVII. fig. 18), including the base of the outer lobe of 
the crown, corresponds in colour, structure and markings with the same part in the 
foregoing tooth, but is somewhat larger, and has had a much larger crown ; it is 
most probably a part of the succeeding grinder in the same jaw, viz. the first true 
molar, m 1 . An extent of 1 inch and 6 lines of the outer enamelled part of the outer 
lobe is preserved, yet the anterior margin of the enamel plate is straight, vertical, and 
the cement covering the anterior surface of the same shows no trace of abrasion from 
pressure against the adjoining tooth, as in p 4 , at the same distance above the lower 
border of the enamel covering the external surface of the anterior lobe. The striae of 
growth are as conspicuous upon the enamel of the present tooth {m 1 ) as in that of 
p 4 ; and there are two transverse rows of punctations. The lower pointed teimiiia- 
tion of the internal plate of enamel is preserved at the back part of the fragment ; it 
is 1 inch 4 lines higher than the termination of the enamel on the fore-part of the 
same tooth. 
The tooth, fig. 18, as the reduced size of the enamel-island a demonstrates, hass 
had more of its crown worn away, has been longer in use than the one, fig. 17; 
which, on the conclusion that it is a premolar (p 4) of the same jaw, must have stood 
in advance of fig. 18; but, though more worn, what remains of the crown of fig. 18 
is longer. The first condition— greater degree of abrasion— accords with the deter- 
