80 CONTRIBUTIONS FROM WALKER MUSEUM 
premaxillary suture the prevomers are free from the side walls of the 
skull, leaving the elongate openings of the posterior nares. The 
sides of the posterior nares are marked on the prevomers by rugose 
ridges. The prevomers are united on the lower surface, but the 
upper portion is divergent, and receives anteriorly the lower edges 
of two vertical plates that seemingly originate from the inner edges 
Fic. 5.—Section of the same skull showing septal bones. Letters as in Fig. 2. 
of the pterygoids and extend directly upward in the skull. Owing 
to the somewhat crushed condition of these very slender plates, 
it is impossible to tell exactly the point of their connection with the 
prevomers below, but apparently they lie between them, and there 
was either a squamous contact, or the bones were free in life and have 
been crushed together in fossilization. The origin of the two ver- 
tical plates is somewhat obscure. They occupy the position of 
vomers behind the prevomers, but the true vomer is a single median 
bone, and, moreover, is accounted for. Broom? has described in 
Proterosuchus two slender vertical plates rising from the inner edges 
of the pterygoids, with a single median vomer between. It seems 
that these plates must be the same sort of a structure. They occupy 
t R. Broom, “On a New Reptile (Proterosuchus fergusi) from the Karoo Beds of 
Tarkastad, South Africa,” Annals of South African Museum, Vol. IV (1903), Art. 7. 
