210 B. NATURAL HISTORY. 
Turning now to those portions of the cranium which are better 
known in allied species, I find the exoccipitals undivided, as did 
Owen in Pt. declivis, and Huxley in Pt. murrayi. I do not even 
find a median suture separating that of the right side from the 
left. Each presents a strong rib extending to opposite the zygo- 
matic arch. The inferior portion is a subtriangular plate, con- 
tinuous superiorly with the rib just mentioned. It is also raised 
Fig. 7.— (Cranium from above.) 
Lystrosaurus frontosus. (Lettering as in figs. 1 and 2.) 
on the median line, and the inferior outline is concave and directed 
downwards. The supraoccipital is vertically ovate, and separated 
from the parietals by squamosal sutures. It does not reach inferi- 
orly to the occipital foramen. 
The parietals viewed from above form together a subquadrate 
plate, with the angles much prolonged; the anterior broadly to 
the postfrontals; the posterior as lamin between the squamosals 
and opisthotics forming the parieto-squamosal arch. They em- 
brace a rather large fontanelle, from which the median suture is 
distinct posteriorly, but invisible anteriorly. 
The frontals are marked posteriorly by a large tuberosity, which 
bounds inwardly a concave surface on each side between it and the 
raised margins of the orbits. These margins are continued poste- 
