296 



CAPT. D. M. S. WATSON ON SEYMOURIA, 



Seymouria in the condition of the brain-case and of the ear. 

 Although their structure could in practically all points be derived 

 from that of Seymouria, they do not in any way recall that 

 reptile. In the Captorhinids we find features which distinctly 

 hark back to the structure of Seymouria, although the group as 

 a whole is one of the most advanced of the Texan Cotylosaurs. 



Through the work of Cope, Broili, Case, and especially Willis- 

 ton, we have a nearly perfect knowledge of the skeleton of both 

 Captorhinus and the more advanced Labidosaurus, and I have 

 given a somewhat more detailed account of the occiput than is 

 to be found in earlier writings. 



The skull of Captorhinus is advanced in the loss of the 

 intertemporal and tabular and 'the very great reduction of the 

 supratemporal ; it retains the primitive feature of a lachrymal 

 reaching the nostril, and of a septomaxilla not appearing on 

 the face. 



It resembles Seymouria in the following important characters : — 



1. The occipital condyle is tripartite, the exoccipitals forming 



a good deal of its surface. 



2. The fenestra ovalis is large, surrounded by the prootic, 



paroccipital, basioccipital, and basisphenoid ; it is 

 placed low down in the skull so that its margin below 

 lies on the border of the tuber basisphenoidalis. 



3. The basisphenoid is remarkably similar in the two 



genera. 



4. The palate of Captorhinus, though advanced in the loss 



of the palatine tusks and in the greater development 

 of the pterygo-transverse flanges, is on the whole not 

 unlike that of Seymouria. 



In the vertebral column the remarkably swollen neural arches 

 of the presacral vertebras and the short nearly obsolete neural 

 spines, are points of resemblance between the two forms. 



The Captorhinids have advanced over Seyinouria in the 

 following ways : — 



1 . In the downgrowth of a process of the paroccipital between 



the lateral margins of the basioccipital and the inner 

 border of the fenestra ovalis, so as to separate that 

 opening more widely from its fellow. 



2. In the reduction of the paroccipital processes and the 



rotation of their ends downwards. 



3. In an enormous widening of the supraoccipital. 



4. In a great deepening of the whole brain-case. 



5. In a reduction of the prootic so that it no longer reaches 



the skull-roof. 



6. In the loss of the tabular and the restriction of the 



dermo-supraoccipital to the occipital surface. 



7. In the loss of the intertemporal and in Labidosaurus of 



the supratemporal. 



