446 The American Naturalist. May, 
10. The external nasal openings are limited by the premaxil- 
laries, maxillaries, and nasals. 
11. The prelachrymal fossæ are large, limited by the maxillaries, 
prefrontals, lachrymojugals. (The suture between jugals ‘and 
lachrymals seems to be very indistinct.) 
12. The orbits are limited by the post-fronto-orbitals, and 
lachrymojugals. 
Ceratosaurus——Mostly after Marsh. 1. The brain-case is not 
ossified in front ; there are no strongly ossified alisphenoids ; this 
region like Sphenodon. 
2. The premaxillaries are separate ; there is no process extend- 
ing between the nasals and maxillaries, excluding the maxillaries 
from the nasal opening. 
3. An epipterygoid (columella). 
4. The jugals are placed in the same level with the alveolar 
border of the maxillaries, and reach the end of the dental series. 
They are in connection withthe lachrymals, postorbitals, quadrato- 
jugals, and maxillary. 
5. The quadratojugal is placed between quadrate and jugal, 
and seems to touch the squamosal. 
6. The squamosal sends down a small process to join the 
quadratojugal. : 3 
7. The quadrate is very much like that of Sphenodon, with a 
foramen between quadratojugal and quadrate, and directed back- 
wards with its distal end. There is a very large ptery goid 
process. ; 
8. Mandible without predentary bone. 
_ 9. Dentary without coronoid process. 
10. The external nasal openings are limited byt 
illaries, nasals, and maxillaries. 
11. The prelachrymal fossz are large, limited by the prefrontals, 
lachrymals, jugals, and maxillaries. 
12. The orbits are limited by the prefrontals, frontals, ne 
orbitals, jugals, and lachrymals. 3 | ae 
By comparing these three forms it is evident that Iguanodon an 
he premax- 
post-fronto- 
stands quite isolated. It shows the peculiar lower jáw, thepeeer a 
