1862.] HUXLEY — CARBONIFEROUS LABYRINTUODONT. 61 



tusk, the alveolar plate, the margin of which is excavated in the 

 interval, affords support to a tooth 0*35 inch in diameter at its base, 

 and this is immediately followed by another of the same dimensions. 

 These teeth are about 0-9 inch long. 



On the right side, the base of a similar palatine tusk and part of an 

 alveolar plate are visible ; but there are no small teeth, and the tusk 

 is situated nearly an inch further back than on the left side. But 

 the alveolar plate extends forward in front of this tusk, and pre- 

 sents a deep sinus, in which I suppose a tusk corresponding to that 

 on the opposite side may have been developed. If the sinus upon 

 the palatine alveolar plate of the opposite side has the same signifi- 

 cation, it would appear as if there were normally two great palatine 

 tusks on each side, but that the anterior and posterior of opposite 

 sides are shed simultaneously. 



The fossil was broken into two pieces when it reached me ; the 

 fracture passing obliquely between the third and fourth teeth on the 

 left side, and through the fourth on the right. The fractured surface 

 shows the roof of the skull, or rather the snout, and proves that it 

 was raised into a broad longitudinal ridge, so convex as to be almost 

 semicircular, about 1*5 inch broad and 0-6 inch above the general level 

 of the facial bones. From the sides of this convexity, the sides of the 

 face slope with a gradual curve towards the alveolar margin. The 

 depth of the skull, immediately over the centre of the maxillary 

 alveoli, is rather less than one inch. From the centre of a line 

 joining the margins of the alveoli to the top of the central ridge is a 

 distance of about 1*9 inch; and in the occipital region the skull is 

 not deeper : considering its breadth and length, therefore, the skull 

 is extremely flat. 



The teeth are round, or slightly oval in section at their bases, 

 and throughout the greater part of their length. They taper gradu- 

 ally to sharp points and become slightly incurved towards their 

 apices. Their bases are not grooved, but, on the contrary, are marked 

 by numerous delicate and sharp longitudinal ridges, so that trans- 

 verse sections appear to be very slightly polygonal. Towards the 

 apex of the tooth, two of these ridges, an anterior and a posterior, 

 become more distinctly marked, and, combined with a very slight 

 flattening of the tooth, give it a double edge. 



In one of the anterior teeth, the front face towards the point is 

 much worn, as if by attrition against one of the mandibular teeth. 



Transparent transverse sections of the teeth exhibit a singularly 

 beautiful and complex structure. The relatively small pulp-cavity 

 sends off primary radiating prolongations, which pass straight to the 

 circumference of the tooth, and at a small distance from it terminate 

 by dividing, usually, into two short branches, each of which gives off 

 from its extremity a wedge-shaped pencil of coarse dentinal tubuli. 

 These spread out from one another, and terminate in a structureless 

 or granular layer, which forms the peripheral portion of the dentine, 

 and, from the small irregular cavities scattered here and there 

 through its substance, reminds one of the ' globular dentine ' of the 

 human tooth. An extension of this peripheral layer is continued 



