OSTEOLOGY OF CAENIVOKOXTS DINOSAURS. 79 



The ])ruicipal differences found by a comparison of the skulls of Ceratosaurus 

 and Antrodemus are contrasted in the two parallel columns below. 



CERATOSAURUS. 



1. Prominent median horn-core on the nasals. 



2. Lateral borders of nasals smooth and rounded. 



3. Skull, relatively narrower, dorso-ventrally 

 than in Antrodemus. 



4. Quadrate, long. 



5. Premaxillary with 3 teeth. 



6. Upper dental series, 18 teeth. 



7. Second antiorbital fenestra appears to be 



.\XTRODEMUS. 



1 . None present. 



2. Lateral borders of nasals roughened and sharp. 



3. Skull, relatively wider, dorso-ventrally than 

 in Ceratosaurus. 



4. Quadrate relatively short. 



5. Premaxillar}' with 5 teeth. 



6. Upper dental series, 20-22 teeth. 



7. Second antiorbital fenestra present. 



wanting. 8- Infratemporal fenestra relatively narrow at 



S. Infratemporal fenestra wide (anteroposteriorly) | bottom, 



at bottom. j 9. External nares elongated. 



9. External nares oval. 10. Nasals without pit. 



10. Pit on posterior median junction of nasals. U. Nasals gradually narrowing. 



11. Nasals, posterior to external nares swollen. I 



Basioccipital (ho.). — The occipital condyle is hemispherical in general form, and 

 is inclined downwards, making an obtuse angle with the long axis of the skull. The 

 basioccipital processes are short and stout, as compared with the narrower and more 

 ventrally elongated ]irocesses in Antrodemus. 



On accotmt of the crushed condition of this region of the skull, the relationships 

 of the basioccipital with adjacent bones can not be accurately determined, though 

 I am inclmed to believe they are somewhat different than in Antrodemus. 



Exoccipital {ex. oc). — The exoccipitals contribute to the upper articular surface^ 

 of the occipital condyle, meeting on the median line and entirely excluding that 

 element from the bomidary of the foramen magnum. It can not be determined 

 whether these bones bridge over the foramen magnum, and thus exclude the supra- 

 occipital from its boundary as they do in Tyrannosaurus. Latterly they coalesce 

 with the paraocci]ntal processes. These processes are more widely expanded 

 vertically toward their outer ends than in Antrodemus, and with a heavier more 

 rugose outer extremity. In the skulls here compared the paraoccipital processes 

 of Ceratosaurus extend more obliquely backward, but this difference may be entirely 

 due to crushing, a point that can not be determuiod. Otherwise the}' are very 

 similar. 



Paraoccipital (p. oc). — The paraoccijiital processes are present, but they are 

 so badly crushed that contrastmg them with others of the Theropoda would be of 

 doubtful value. From what can be observed of their form and relationships they 

 appear to be very similar to those of Antrodemus, except that vertically their outer 

 ends are ntore widely expanded and more rugose than in that genus. 



Supraoccipital {so.). — On account of the crushed condition of this portion of 

 the occipital region and the coalescence of the sutures the boimdaries of the supra- 

 occipital can not be determined. 



Alisphenoid {al. sp.). — The distorted condition of the alisphenoids and the 

 coalescence of the sutures in the Ceratosaurus skull render the comparison of this 

 element with those of other Theropod reptiles of little value. 



