On Ictidosuchus Primevus. 179 
resemblance to the corresponding bone in previously known 
Theriodonts, it has a number of characters that are quite distinctive. 
The anterior dentigerous portion has a moderately flat surface and is 
even slightly concave at its lower border, but is remarkable by having 
numerous small irregular cuplike depressions, which give the bone a 
rough appearance at this part. The posterior non-dentigerous part, 
which is of moderate size, though showing very marked longitudinal 
striz, has the surface of the bone smooth and even polished. The 
teeth comprise one large canine and a row of small simple molars. 
In the maxillary as preserved there are the remains of eight molars, 
and one is probably lost. Unfortunately the anterior three teeth are 
crushed backwards on the others, and of all the crowns are wanting. 
Fortunately in the detached right maxilla the crowns of three teeth 
are preserved, and show them to have been simple cones with the 
sides of the teeth ridged. The molars are all subequal in size. The 
canine is of relatively large size and directed mainly downwards. 
The fragment of maxilla which contains the root of the canine, 
though it cannot be fitted on to the larger portion of the maxilla, 
is figured in its exact relative position, the cast of the maxilla having 
fortunately been kept. 
The jugal bone is a somewhat slender bone which probably forms 
the whole of the suborbital arch, and possibly a considerable portion 
of the temporal arch. 
Of the palate it is impossible to speak with any degree of confi- 
dence. The little that remains in connection with the maxilla of each 
side is so crushed and imperfect that but a very unsatisfactory idea 
can be formed of the original condition. It may be regarded as 
moderately certain, however, that there is no distinct secondary 
palate such as is seen in Cynognathus. The maxillary only shows 
to a very small extent internal to the molar teeth, and joins what is 
apparently a forward extension of the palatine bone. 
The lower jaw is fairly well preserved; almost the whole of the 
dentary element, with most of the teeth, having been found. It is 
characterised by the remarkable slenderness of the ramus and by 
the greatly developed coronoid process. In the large majority of 
Theriodonts hitherto discovered the lower jaw is a powerful bone 
with a deep symphysis. Tribolodon, however, agrees with Icti- 
dosuchus in having a slender ramus, though the two genera are 
probably very dissimilar in most points of structure. In the jaw as 
preserved there are the remains of seven teeth, for the most part in 
good condition. They are all situated near the middle of the ramus, 
and, like the molar teeth above, are subequal in size. From the 
posterior third of the ramus teeth are undoubtedly absent, and from 
