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Show 478 MR. G. A. BOULENGER ON THE [APr- ^> ground of the articulation of the skull with the atlas by a pair of cotyles in the basioccipital bone, corresponding in position with the Mammalian occipital condyles, whilst the median part of the bone, which forms the floor of the foramen magnum, is produced in the position occupied by the median occipital condyle of Reptiles. Cope alludes at the same time to an " enormous frontoparietal foramen." In Cope's classification of 1889* the Cotylosauria are defined as Theromora with the coracoid reduced, not meeting the sternum, the ribs single-headed, the temporal fossa " overroofed," the dentition "abundant," and intercentra present. The Pario-sauridaa are included in addition to the Diadectidaa; and in his last contribution, " The Reptilian Order Cotylosauria," t the Elginida-and PariotichidaB J are also added, the former of which appear, from our present, imperfect knowledge, to be close allies of the Pariosauridse, without any special affinity to the Diadectida?. The restoration of the very imperfect upper part of the skull of Diadectes and allies, as originally given by Cope §, is not to be relied upon, since the illustrious American palaeontologist, in his later writings, defined the Cotylosauria as with the temporal region entirely roofed over by bone. That a small supratemporal fossa might have existed appears from the following brief statement recently made by Case ||:-" It is of interest to note that the author discovered perforations in the roof of the skull of the Diadectida? in the Cope Collection in the position of the superior temporal vacuities; the forms are too specialised to make the interpretation of this occurrence certain, but it m a y well be the first step towards the Proganosaurian type." Dr. Case, has however, since written to m e (Dec. 12, 1903) that these vacuities do not occur in a second specimen from the same region in the Cope Collection. H e kindly adds :-" The skull of the Diadectids is very rugose and the sutures are very obscure ; there are certainly no distinct temporal arches and the position and limits of the bones of the temporal region is uncertain. The whole region was covered by a complete roof in all the specimens but the one noticed, and the quadrate is closely connected with the roof-bones, so that the whole region has a strong superficial resemblance to the turtles." Dr. Case has ascertained, moreover % that the pectoral arch of the Diadectidse consists of scapula, coracoid, pre-eoracoid, clavicle, and interclavicle. Cope ** has given a very brief description of a Diadectid pelvis, which agrees in all essential characters with that of Procolophon and Telerpeton. * Amer. Natur. xiv. p. 304. In this classification, the Procolophonidw arc placed in the incongruous assemblage Proganosauria. t Op. cit. xxiii. p. 866. X E. T. Newton, Phil. Trans, clxxxiv. B, 1893, p. 473; E. C. Case, Zool. Bull. ii. 1899, p. 231. § Proc. Amer. Philos. Soc. xix. 1880, pi. v. || Amer. Natur. 1903, p. 99, footnote. f Amer. Journ. Geol. xi. 1903, pp. 397 & 400. ** Proc. Amer. Philos. Soc. xx. 1882, p. 448. |
