TAB. XVI. 



Plesiosaurus Hawkinsii, nat. size. 



Fig. 



1. Oblique side view of skull. 



2. Under view of skull. 



In comparison with the skull of Plesiosaurus dolichodeirus, Tabs. II and III, 

 tbese figures exemplify the specific distinction of Pies. Hawkinsii in the greater 

 longitudinal extent of the temporal fossse, and in the greater relative length and 

 slenderness of the muzzle or facial part of the skull, the sides of which converge 

 at a more acute angle and are more concave. The symphysis of the mandible 

 is longer in PL Hawkinsii. The teeth in both jaws are relatively larger and longer 

 in Plesiosaurus dolichodeirus. As compared with Plesiosaurus rostratus, Tabs. IX 

 and XIII, the facial part of the skull is relatively shorter in Plesiosaurus Hawkinsii ; 

 the pterygoids do not extend quite so far back; the " palatonares," Tab. XVI, 

 fig. 2, r, r, are smaller, with more rounded ends of the ellipse. 



The following bones are indicated by the figures : 



1. Basi-occipital. 



2. Par-occipital. 



7. Parietal (near the "foramen parietale"). 

 7'. lb., " supra-mastoid process." 



8. Mastoid. 

 11. Frontal. 



15. Nasal (above the external nostril). 

 20. Palatine. 



24. Pterygoid. 



25. Ecto-pterygoid. 



26. Malar. 



27. Squamosal. 



28. Tympanic. 

 31. Angular. 

 31'. Splenial. 

 33. Dentary. 



The skulls here figured are from the Lias of Street, Somersetshire. In the 

 British Museum. 



