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Show 18 MR. F. E. BEDDARD ON THE [Jan. 17, posterior limbs of that bone in the three types under consideration a re :- Physignathus ................ 10 : 16 Chlamydosaurus............ 5 : 14 Amphibolurus................ 6 : 17 Chlamydosaurus and Amphibolurus are thus much closer together than either is to Physignathus. The parietal foramen is quite different in the three types. In Physignathus it is very minute; in Amphibolurus it is large and longitudinally oval, and the suture between the frontal and parietal bones touches the foramen equatorially. In Chlamydosaurus the foramen lies much further back and is quite in the middle of the anterior median piece of the parietal bone ; it is intermediate in size between the foramina of the other two types. The occipital region of the skull is much more depressed below the level of the posterior limbs of the parietal in Physignathus than in the two remaining genera. Anteriorly the dorsal aspect of the skull shows differences in these Agamid Lizards. In both Chlamydosaurus and Amphibolurus the premaxillary bone extends back beyond the posterior level of the nostrils. In Physignathus the bone, which is broader than in the other two types, does not extend so far back as to the posterior boundary of the nostrils; it follows that more of the nostrils are bounded by the nasal bones in Physignathus than in its allies. On the palatal aspect of the skull, Chlamydosaurus shows a peculiarity which is not shared by either Amphibolurus or Physignathus ; that is, that the palatines fail to meet in the middle line except for a short space anteriorly. This is not a matter of deficient ossification, as is shown by the clear rounded margins which bound the area where the palatines do come into contact. There is no question, however, here of the pterygoids pushing their way in between the palatines and preventing the latter from articulation, such as I have recently called attention to in Urornastix spinipes*. In none of these Lizards is there a distinctly separate postfrontal bone ; nor can I detect between the occipital and the first supra-temporal any rudiment of the second supratemporal. In all three genera, as well as in Urornastix, the columella (epipterygoid) does reach the parietal bone above; inasmuch as this bone does not reach the parietal in Iguana (as noted by Shufeldt t ) or Phrynosoma, it seems likely that this character will prove useful in distinguishing the two families Agamidse and Iguanidse. In all three genera- Chlamydosaurus, Amphibolurus, and Physignathus-the quadrate is directed backwards. In Iguana, on the other hand, it is nearly straight, that is, at right angles * Supra, p. 3. f " Contributions to the Study of Ueloderma," P. Z. S. 1890, p. 222. |