On Ictidosuchus Primevus. 183 
expanded lower end, so that the inner side of the concave lower end 
is really an anteriorly directed ridge, which stands prominently out 
from the femur. 
. TrB1A AND FIBuLa. 
The tibia is fairly well preserved, but only a portion of the fibula 
remains. The tibia is a moderately long bone of fairly uniform 
thickness, considerably expanded at its upper end and slightly at its 
lower. It resembles the tibia in Marsupials in being flattened 
laterally. Near the union of the middle with lower third the axis of 
the bone is bent slightly backwards. The fibula near the middle is 
about half the thickness of the tibia, but at its lower end it becomes 
considerably expanded. 
VERTEBRE. 
One or two vertebra have been found, but not in a very satisfac- 
tory condition. The bodies of the vertebrze are biconcave, but not 
very deeply cupped, and the arches remain united with the bodies 
only by suture. The length of the body is one of the best preserved, 
and probably a dorsal vertebra is 15 mm. 
UNDETERMINED ELEMENTS. 
Two moderately well-preserved bones I have thought it advisable 
to figure, though I cannot venture on an opinion as to what they 
are. The first is a somewhat triangular little bone, from one angle 
of which passes out a long, delicate, perfectly flat bony process. 
This process has evidently lain alongside of some element which 
fitted into a deep groove on the same side of the triangular bone as 
the process ; and the element which has fitted into the groove has 
been held in position by an overlapping plate of the triangular 
element. | 
The other bone is moderately flat, and has passing out on one side 
also a long bony process, but a slightly twisted one. 
As there is no evidence as to the relations of these bones, I think 
it inadvisable to speculate as to what they may be. 
CONCLUSIONS. 
From the examination of the various remains of Ictidosuchus it 
will be seen that, though the form is a Theriodont, it differs very 
considerably from most known Theriodonts, and in a number of 
points shows affinities with the Anomodonts, and it is not improb- 
able that it may belong to that group of primitive Theriodonts from 
which Dicynodon and its allies appear to have sprung. 
Ictidosuchus is probably allied to Theriodesmus, but the structure 
of the tibize shows the two genera to be quite distinct. 
