28 CASE. [Vou. XIV. 
extends farther back on the lower surface than on the upper, 
and its posterior part is marked by a deep pit. The dentary 
reaches very nearly to the posterior extremity of the man- 
dible, covering in large part the complementary and the sur- 
angular. 
The complementary is present and complete; it is largely 
covered externally by the dentary, which also overlaps the 
superior margin, and appears on thé supero-internal edge. The 
posterior end rises rather high, and terminates abruptly. Its 
postero-inferior angle articulates with the angular, and forms a 
bridge over the cavity in the ramus. 
The presplenial. Dr. Baur has drawn my attention to the 
fact that the element described by him (44) in the jaw of cer- 
tain pleurodiran turtles (the group Chelyotdea), in the Croco- 
dilia, and in the Lacertilia as the presplenial, also occurs in 
Protostega and Toxochelys. It is an elongated element articu- 
lating with the angular and splenial behind, the dentary below, 
and the coronary above, occupying the same position as in the 
Chelyoidea, but extending far forward, and covering the groove 
on the internal surface of the ramus except in its anterior extent. 
It is pierced by a foramen near its anterior edge. Its general 
form and relations are shown in the accompanying figure. 
weil ae. 
. Dr Dice Vo 
94 89935 : 
wisn IY > 
B20, 920 2S 
The sflenial is distinct from the angular, and appears as a 
long, splint-like bone reaching forward towards the symphysis. 
It appears largely on the under surface of the mandible. 
The angular is short and broad; it sends a process upwards 
to meet the complementary. The posterior end shows a large 
face concave from above downwards, and looking almost 
directly backwards. It rises above the surangular, concealing 
it on the interior aspect. 
