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Show 112 MR. G. A. BOULENGER ON THE OSTEOLOGY OF [Jan. 20, more or less developed, in the Ophidians. As observed by Shufeldt, the bony dermal tubercles of the head are so intimately adherent to the bones that it is extremely difficult to remove tbem in adult specimens : but in the half-grown skull of H. horridum, which is quite as large as that of the adult H. suspectum, they could be detached very readily, and the skull shows all the sutures perfectly distinct, as correctly figured by Gervais and by Bocourt *. I may add that bony tubercles are also present on the dorsal and lateral Skin of the middle part of the body of H. suspectum, epidermis removed, showing the bony tubercles ; nat. size. surfaces of the body, but wide apart and gradually diminishing in size towards the ventral surface, which is entirely devoid of dermal ossifications or shows mere ring-like traces of them, except on the prseanal region, which, like the back, is studded with bony tubercles. Vertebral Column. This consists of 8 cervical, 26 dorsal, 2 sacral, and 40 caudal (=76) vertehrse in //. horiidvm, of 8 cervicals, 26 or 28 dorsals, 2 sacrals, and 27 caudals ( = 63 or 65) in H. suspectum. In the (2 ) specimen of the latter species, with 28 dorsal vertebrae, both centrum and arch of the 21st vertebra are anchylosed with the 22nd. I was anxious to examine the atlas, as I had been much struck by Dr. Shufeldt's statement (P. Z. S. 1890, p. 214) that it is " composed of five separate pieces; three of these are devoted to the formation of its anterior cup for the cranial condyle. Of these three pieces, one is a mid-ventral one, while either of the others are ventro-laterally situated. Each side of the neural arch is formed by one of the two of the remaining pieces of the five of the component elements of this vertebra ; and in a large specimen of this lizard none Miss. Sc, Mex., Kept. pi. xx. E. |