234 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 92 
Frontal.—The frontal (/) region of the type is checked and broken, 
so that much of the description is based on the better-preserved fron- 
tals of U.S.N.M. Nos. 15568 and 15816. In these specimens they are 
distinctly separate along the median line, but in the type specimen 
they are coossified. Their anterior ends unite with the nasals by a 
V-shaped suture that indents the ends of the frontals. Laterally the 
frontal articulates with the prefrontals and postfrontals much as in 
Glyptosaurus. ‘The anterior and posterior processes of the post- 
frontals and prefrontals do not meet above the orbit but are separated 
by an interval of 6.5 mm. This space constitutes the frontal contri- 
bution to the boundary of the orbit. The lateral border above the 
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Ficure 16.—Skull of Polyglyphanodon sternbergi Gilmore, U.S.N.M. No. 15477, type, natura 
size, viewed from the right side: an, Angular; ar, articular; c, coronoid; d, dentary; exo, 
exoccipital; f, frontal; 7, jugal; Ja, lachrymal; mx, maxillary; na, nasal; 0, orbit; p, parietal; 
pf, prefrontal; pmx, premaxillary; po, postorbital; pif, postfrontal; gu, quadrate; sa, 
surangular; smx, septomaxillary; sg, squamosal; ta, tabulare. 
orbit is beveled from above downward and inward. On the ventral 
side, as shown by specimen U.S.N.M. No. 15559, the lower edge of the 
beveled surface forms a low-curved ridge that extends from one end 
of the bone to the other. The ridge becomes more prominent toward 
the anterior end, forming the lateral boundary of the olfactory portion 
of the brain. Between the orbits the frontals of the type specimen 
have a least transverse diameter of 10 mm. The dorsal surface is 
ornamented by a series of alternating transverse ridges and 
depressions. 
Nasals.—The nasals (na) are irregularly shaped bones with long, 
slender anterior extremities that embrace the long posteriorly di- 
rected spine of the premaxillary, as shown in Boas 17. Laterally 
the frontal articulates entirely with the maxilla, being excluded 
from contact with the prefrontal by the interposition of the slender, 
