Pomona College, Claremont, California 59 
has no especial markings or features other than the impressions 
made by the bones which come in contact with it. On its ventral 
surface are two long narrow impressions left by the squamo- 
palatines. 
The sphenethnoids (12) are the bones which serve as walls to 
hold apart the dorsal and ventral surfaces of the skull. They are 
rather long bones, about three-fourths as long as the parasphenoid. 
They articulate posteriorally with the occipitals, their dorsal edge 
articulates with the frontals and parietals, their ventral edge with 
the parasphenoid. Anteriorally they bound a portion of the open- 
ings into the occipital fossae. 
The mandibles of Notothalamus torosus are each composed of 
two bones, the dentary and the articulare. 
The dentary (14) is that part of the mandible which bears the 
teeth. It is a long slender, curved bone, articulating anteriorally 
with the other dentary, and widening out posteriorally to articulate 
with the articulare. 
The articulare (15) is that part of the mandible which diverges 
posterioraily to form a rounded knob which fits into the articular 
socket of the quadrate. Anteriorally, on the median side it fits 
down into the dentary bone. 
