24 DK. R. BttOOM ON THE 



functions. The tabular is a mucli more important element. 

 Besides being a bone of the top of the skull, it is also an occipital 

 element with important bony and muscular attachments. The 

 supratempoi-al is apparently very rarely, if ever, an occipital 

 element at all. For these and other i-easons which I am else- 

 where giving, I regard the upper element in all the later reptiles 

 in which it occurs as the tabular. 



In Mixosaurus, Gymhosponclylus, and Ichthyosaurus the back 

 of the temporal fossa and much of the occipital margin is formed 

 by the tabular. The squamosal is situated below it. The 

 relations of the two bones are strikingly similar to those in 

 lizards. 



For the discussion of the temporal region in the two-arched 

 reptiles we are very fortunate in having two good skulls of an 

 animal that must be pretty near to the ancestral type. Younyina 

 capensis, which I described a few years ago, is too specialised in 

 having a long snout to have itself been the Diapsid ancestor, 

 but it is sufficiently near for all morphological purposes. The 

 temporal region is remarkably interesting. The squamosal is 

 large and lies almost entirely behind the infratemporal fossa. 

 Above the squamosal lies a bone which I think there can be 

 little doubt is the tabular. It is situated between the parietal 

 and the squamosal. The relations of the bones will be best 

 understood from the figure given. Whatever doubt there might 

 have been about the identification of the squamosal in the type- 

 skull is removed by the second skull which I was fortunate in 

 discovering. This second skull, though it lacks the occiput, has 

 the snout well pi-eserved. 



The Thalattosauria form a group of very remarkable marine 

 reptiles, which seem to have some affinity with the lizards and 

 Sphenodon. Unfortunately, they are very imperfectly known. 

 Merriam, who first described them, gave good figures of the 

 specimens and attempted restorations of the skull. Huene, who 

 has since examined the material, diflfers from Merriam in the 

 interpretation of some of the parts of the temporal region. The 

 most important difference of opinion is that Huene considers 

 that the squamosal of Merriam is really the supratemporal, and 

 finds the true squamosal in a much smaller bone situated below 

 the larger bone. I am inclined to think that in this Huene is 

 probably right. I give a restoration of the skull, modified from 

 Merriiim in the light of Huene's later observations, and with 

 the occiput restored as I think it may have been. If this 

 figui-e be compared with that of Younyina (text-fig. 4, A &, B), it 

 will be seen that Thalattosaurus is strikingly similar in type, 

 but specialised in a manner curiously parallel to that seen in 

 the primitive Ichthyosamvs Cymbospondylus and Mixosaurus. 



The Lacei-tilia have given rise to much difference of opinion, 

 not only as to which of the two post-temporal bones is the 

 squamosal, but also as to whether they are really descended from 

 ancestors with two temporal fossee. It has long seemed to me 



