THE CRANIAL OSTEOLOGY OF RHIZODOPSIS. 175 
of the mandibular elements of this genus. The depth of this jaw is 1,3, 
inch ; its entire length, including the impressions of its anterior and posterior 
extremities, is 54 inches. The upper edge of the dentary element is seen 
extending from the obtuse angle of the posterior extremity of the upper aspect 
of the jaw to where it is broken off, apparently 14 inch from its symphyseal 
termination, as indicated by the impression, and is set with a single row of small 
conical teeth, placed on an average at distances from each other of + inch, 
though they are more closely set anteriorly, where a few empty sockets are also 
seen. Some of the hinder ones are entire, and measure 3} inch in length; they 
are sharp, slightly incurved, their bases plicate, the surface fretted with very 
minute striz, visible only under a strong lens. Anteriorly they are all broken 
off at various heights, the sections showing a large internal pulp cavity, the 
walls of which become very simply plicate at the base. Now, articulated just 
below this dentary margin is a longitudinal chain of two separate ossicles and 
the hinder part of a third. Each of these (én. d.) is of an oblong shape, con- 
tracted at the extremities, and in the middle showing first an empty socket, and, 
immediately in front of this, the broken off root of a large laniary tooth, at once 
recognisable by the complex folded structure of its constituent dentine. The 
anterior of these ossicles is obliquely broken off right through the empty 
socket, at the bottom of which are the remains of dentinal plice, showing how 
here too a large tooth had once existed and had been broken off; and in front 
of this, and just above where the root of the actual laniary had been, is a part 
of the impression, upon the matrix, of the very tooth itself. Nothing can be 
more distinct than the sutures which separate these accessory or internal 
dentary ossicles from each other, and from the contiguous dentary element 
proper—the remaining bony matter beneath, consisting of the plates previously 
referred to as angular and infradentary, is thin and traversed by numerous 
cracks and fractures, so that very careful examination is here required for 
the determination of sutures. Nevertheless, with due attention, the lines 
of demarcation between the angular and the two large infradentaries may 
be made out, and just behind the position of the symphysis there is an 
indication of another suture passing upwards and forwards from the lower 
margin of the jaw, and separating off the third and smaller infradentary 
already alluded to. Lying on the margin of the slab, 24 inches from the above- 
described jaw, is a broken-off piece of bone having a large tooth attached to 
it, the latter measuring 2 inch in length by 1 inch in diameter at the base. Its 
length was originally in all probability greater, as it is obliquely fractured, and 
the fractured surfaces ride over each other a little. Its base is plicate, above 
which the surface of the tooth is very minutely and delicately striated up to 4 
inch from the point, which is perfectly smooth. Close beside this large tooth, 
and apparently attached to the same piece of bone, are two smaller ones, each 
VOL. XXX. PART I. 2D 
