1905.] 



PRIMITIVE REPTILE PROCOLOPHON. 



223 



relation of the occipital and qiiadiute regions is Pareiasmi,ru,s ; 

 but the large lateral perforations in the occiput and single con- 

 dyle for the occipital articulation prevent close comparison with 

 Procolophon. There is a similar approximation to the condition 

 in some Labyrinthodonts in this relation of the two parts of the 

 occipital region, but in most of those types the occipital plate 

 inclines obliquely forward, and is not comparable in the details of 

 structure of the skull. In no Dicynodon or Theriodont is there 

 any approximation to Procolo^ihon in this region of the skull, 

 except in the occipital plate being usually imperforate. 



Text-fie-. 32. 



Type specimen of Frocolojphon laticeps, from Donn3brook, showing (ff) the vertical 

 occipital plate and {h) the postorbital foramen. 



The specimen figured in 1889 (Phil. Trans, pi. 9) as Proco^jAow 

 trigoniceps was thus identified, as I now think, in error, because 

 the matrix was not then removed from P. laticeps. From its 

 excellent pi-eservation Di-. Exton's fossil has been referred to as 

 the type of Procolophon. That skull is exceptional in showing a 

 distinct lateral postorbital foramen between the squamosal, post- 

 orbital, and malar bones. When originally desciibed, the vacuity 

 was regarded as being in the position of the supra-temporal 

 bone, which was supposed to have disappeared as in Crocodiles, 

 leaving a postorbital vacuity. Dr. Smith Woodward speaks of 

 it (Verteb. Pala^ont. p. 148) as evidently the beginning of a 

 lateral temporal vacuity, and this view is adopted by Prof. Osborn 

 (Mem. Amer. Mus. vol. viii. p. 480). Whatever may be the value 

 of the character, it is absent from Owen's types, as already 

 remarked. It is only found among described species in P. laticeps, 



Proc. Zool. Soc— 1905, Vol. I. No. XV. 15 



