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Show 1 9 0 5 .] PRIMITIVE REPTILE PROCOLOPHON'. 2 2 3 relation of the occipital and quadrate regions is Pareiasaurus; but the large lateral perforations in the occiput and single condyle 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 Procolophon in this region of the skull, except in the occipital plate being usually imperforate. Text-fig. 32. a b Type specimen of Procolophon laticeps, from Donnybrook, showing (a) the vertical occipital plate and (b) the postorbital foramen. The specimen figured in 1889 (Phil. Trans, pi. 9) as Procolophon trigoniceps was thus identified, as I now think, in error, because the matrix was not then removed from P. laticeps. From its excellent preservation Dr. Extoii'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, postorbital, and malar bones. When originally described, 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. Palaeont. 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, P r o c . Z o o l . Soc.- 1905, V o l . I. No. X V . 15 |