220 



PROF, H. G. SEELEY ON THE 



[Mav. 21, 



markings already referred to, which appear to indicate a posterior 

 division of the parietal bones, really indicate bones, they would 

 represent the pair of ossifications termed supraoccipital in 

 Labyrinthodonts, over which the parietal bones may extend. 

 Procolophon may thus far be crypto- Labyrinthodont in the struc- 

 ture of this part of the head. In Pareiascmrus there appears to 

 be a narrow bone behind the parietal bones (Phil. Trans. Royal 

 Soc. 1888, p. 69) and also a pair of bones behind the squamosals, 

 postsquamosal bones as they may be named, which are in the 

 position of the bones previously termed epiotic. The preservation 

 in Pareiasaurus of this region of the skull leaves much to be 

 desired, but it suggests comparison with Procolophon. 



Text-fio-. 31. 



Tj'pe specimen of ProcoJopJion trigoniceps, from Doniij'brook. 

 For comparison with P. minor. 



The Postorhital bar. — The preservation of the type of Procolojihon 

 trigomceps (text-fig. 31) is not quite satisfactory, owing to cranial 

 l^ones having scaled ofi" from the fi-ontal region and the postoi'bital 

 area on the right side. On the left side there appears to be a slight, 

 almost imperceptible linear separation between the postorbital and 

 the squamosal and quadrate bones. It might pass as a condition of 

 f ossilization, since it is absent in P. minor, but for the circumstance 

 that the condition becomes a foramen in P. laticeps (text-fig. 32). 

 There is no trace of the slit on the right side of the skull. There 

 the sutural lines indicate a long narrow strip of bone descending 



