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Show 1905.] OSTEOLOGY OF THE MASTIGURE LIZARD. 7 That half of the supposed squamosal which is applied to the parietal rests upon a thin splinter of bone which is, I think, but am not quite certain, continuous beneath with the cut off portion of the supposed squamosal. The latter therefore evidently consists of two quite separate parts, which are not distinguished in Gegenbaur's figure already referred to. The question is, what are these two bones ? but, before attempting to answer it, we will consider the same region of the skull of Iguana which is figured (not very satisfactorily) in Bronn's ‘ Thierreichs ' *. In that lizard (see text-fig. 4, B, p. 8) a rounded bone lies between the parietal, occipital, quadrate, and reputed squamosal. This bone may be the segmented-off' portion of the squamosal complex in Uromastix, or it may be the tiny bone in the same lizard which lies (see text-fig. 4, C) closer to the occipital, and which must be a supratemporal. If we compare the arrangement of the bones in the squamosal region of Uromastix with that in Lacerta as figured by Parker t, it would seem that we have, as in that lizard, two supratemporal bones of unequal size : the smaller of these is that wedged in close to the occipital; the larger is the external bone overlapping the real squamosal and commonly termed squamosal. Parker observes + that " in many kinds (of lizards) . . . . the first supratemporal is wanting, the second is constant." If by the latter half of this statement the constant presence of a separate second supratemporal is meant, I venture to disagree with Parker. It does, however, apparently exist commonly, and is figured, for example, in Gerrhonotus by Siebenrock §. I use the word " apparently" advisedly; for I am not yet convinced that the bone in question is not in reality, as I have already suggested, the squamosal. I may point out that the way in which I have ventured to interpret the bones of the region of the skull is quite in accord with Shufeldt's description of the skull of Heloderma ||. In this lizard, Shufeldt describes as squamosal the bone which I have so named in Uromastix spinipes, and describes as a " fragment of the hinder end of the zygomatic arch " a rudiment which undoubtedly corresponds with the squamosal multorum auctorum. I detect in a specimen of Heloderma forming part of the collection in the Society's prosectorium (text-fig. 4, D, p. 8) a bony nodule lying between the occipital and the squamosal, which I identify with the second supratemporal of Lacerta and of Uromastix spinipes. Siebenrock 51 has come to the same conclusion with regard to the bone that is in my opinion to be regarded as the true squamosal. But he terms that bone which I venture here to call supratemporal, " Paraquadratum." He does not appear to have seen * Vol. vi. Reptilien, Taf. 68. f. 7. f Phil. Trans. 1879, pi. 42. fig. iv. J Loc. cit. p. 599. § " Zur Kenntniss cl. Kopfskelet. d. Scincoiden," Ann. k.-k. Hofmus. Wien, vii. ^ || " Contributions to the Study of Heloderma smpectum," P. Z. S. 1890, p. 148. If " Das Skelet der Agamidie," SB. k. Akad. Wiss. Wien, civ. p. 1112. |