238 MEMOIRS OF THE CARNEGIE MUSEUM 
the prefrontal bones along the anterior portion of their hind margins, the prefrontals 
being coneavely bevelled at their extremities like the frontals, in order to receive 
them. 
The Maxillary (Fig. 3 and Plates XXIII, XXIV. and XXVI.).—The maxillary 
is very largely developed and consists dorsally of a thin bony plate of irregular 
triangular outline forming the greater portion of the superior surface of the exter- 
nal walls of the facial region of the skull. On its ventral aspect it sends inwardly 
from its outer margin a broad lower plate, throwing out two long backward proc- 
esses the innermost of which articulates, according to Professor Marsh, with the 
vomer, and the outermost of which articulates with the palatine, according to the 
same author. 
The Premawillaries (Fig. 3 and Plates XXIII., XXIV. and XXVI.).—The pre- 
maxillaries are paired subtriangular bones, occupying the triangular space in front 
of the skull between the maxillaries. They consist of an upper and lower bony 
plate. In all specimens examined by the writer the number of teeth in each pre- 
maxillary is four. 
Premaxillary Processes (Fig. 3 and Plates XXIII., XXIV. and XX VI.).—Ranging 
backward from the premaxillaries, located between the maxillaries, are the two long 
slender bones, which Professor Marsh interprets as backward prolongations or proc- 
esses of the premaxillaries, but which may be regarded as lateral ethmoids. ‘These 
bones on the median line of the skull unite to form a raised ridge, which is higher in 
front than behind. At the anterior point of commissure the bones widen outwardly 
somewhat and terminate in blunt, outwardly obliquely truncated ends, which are 
raised above the level of the premaxillaries and maxillaries. There are at this point 
two moderately large foramina, one on either side, the purpose of which is yet to be 
determined, but which correspond more nearly in location to the nares as ordinarily 
found in the reptilia than any other openings in the skull. 
Pterygoids, Palatine, and Vomer. — Professor Marsh’s description of these bones 
was evidently based upon studies made by him after having taken the specimen 
(U.S. N. M., No. 2678) apart, so as to permit of a satisfactory examination of the 
roof of the mouth. At the time when the specimen was returned to the United 
States National Museum it was in separate pieces, and these have been reassembled 
so that it is now impossible to make a minute examination of the bones referred to, 
more particularly the palatine and the vomer. There is no reason to question the 
essential correctness of the brief descriptions and the figures given by Professor Marsh. 
The Dentary (Fig. 3 and Plates XXTUII. and XX VI.). — In the figure of the lower 
jaw given by Professor Marsh, ‘ Dinosaurs of North America,” Plate XXV., Fig. 1, 
