PROTOSTEGID&. 205 
_Points to be especially noted in this skull are its long and narrow form, the long preorbital 
region, the hookt beak, the posterior position of the orbits, and the upwardly directed nasal 
opening. Contrary to what is usually seen in turtles, the orbits are placed in the middle of the 
pa 
—— pos 
= 
CONG 
sith: ju den 
Fic. 263.—Archelon tschyros. Skull. x4. 
ang, angular; art, articular; den, dentary; fr, frontal; ju, jugal; mx, maxilla; nar, nares; prf, prefrontal; pal, 
palatine; pmx, premasilla; pa, parietal; pof, postfrontal; qu, quadrate; guj, quadratojugal; $q, Squamosal; 
st, stapedial rod; sur, supraangular; vom, vomer. 
length of the head. This results from the great development of the preorbital region. The 
horizontal diameter of the orbit is 150 mm. ; 
Both the maxilla and the premaxille are greatly prolonged. The distance from the tip 
of the beak to the anterior rim of the orbit is 240 mm.; from the orbit to the suture between the 
pia 
vol 
cho 
Hts 
up 
fl \ 
“pu = ee: = 1 
ys 7 pm 
von 
Ne. pal. mu 
pt 
Fics. 264 and 265. Archelon tschyros. Skull. 
264. Palatal surface. X,'g. bsp, basisphenoid; cho, cho- 
—bsp ane; ju, jugal; mx, maxilla; oc, occipital condyle; 
pal, palatine; pmx, premaxilla; pt, pterygoid; qu, 
“a quadrate; guj, quadratojugal ; sq, squamosal; vom, 
qu vomer ; vp, vomero-palatine region. 
265. Side view of front. X}. mx, maxilla; nar, nares; 
-sq o, orbit; pal, palatine; pmx, premaxilla; prf, pre- 
frontal; vom, vomer. 
maxilla and the premaxilla is about 150 mm. The tip of the premaxilla is bent down at nearly 
a right angle with the axis of the skull, forming a great hawk-like beak. 
The nasal opening 
looks wholly upward. Its length is 120 mm.; its width, 70 mm. 
