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Show 234 DR. R. W. SHUFELDT ON [Apr. 1, skeleton of a Heloderma. Indeed, if we take the skulls of Iguana tuberculata. and Crotaphytus collaris it is not a difficult matter to pick out quite a number of points of near resemblance. From all that I have seen in the works of other authors, 1 am strongly inclined to believe that when the morphology of such species that are now grouped in the genera Xantusia, Xenosaurus, and Lepidophyma is thoroughly worked out, no inconsiderable amount of light will be thrown upon the subject of the affinities of the Heloder-matidai. So far as our present knowledge of existing reptiles extends, I am convinced that it is in the direction that I have just indicated that we must look for the affines of our Heloderma suspectum. When we come to consider the group of characters that are presented us on the part of the form to the anatomy of which the pages of this memoir have been devoted, there can be but one opinion in our minds as to the classificatory rank that should be awarded to the Heloderm in the system. For a great many years zoologists have met all the way through the animal series forms the taxonomic arrangement of which demanded a somewhat higher rank than the genus seemed to suggest. This need seems to have been quite thoroughly satisfied in the creation of the subfamily, as it is now generally employed and has been so long in use. On the other hand, at a considerably later date, the necessity for a group ranking higher than the family became apparent, and this was first met by Gill, who in 1872 introduced the use of Superfamilies x ; and they have been steadily growing in favour with naturalists ever since. The same zoologist has already created a superfamily to contain the Heloderms. This he has termed the Helodermatoidea, and has selected the following characters to designate it, viz.:-" Eriglossate Saurians with concavo-convex vertebrae ; clavicles undilated prox-imally, and post-orbital bony arches, but without post-frontosquainosal arches " (Smithsonian Report, 1885, pt. i. p. 800). The Helodermatidce is the only known family of this superfamily, and it, as we now know, contains but the two species which have been referred to in this memoir. They are the only ones at present known to science. To return to the taxonomy of them, the present writer is of opinion that the morphological characters presented on the part of these reptiles, which characters have been set forth in detail in this work, go to support the classification suggested by Gill, and it is proposed, in so far as it applies to the definition of the Heloderms in the system, that the arrangement be adopted. It is adopted here. Many things have, during my studies of the Helodermutidce, inclined me to believe that these reptiles are probably derived from a rather old stock, and that during comparatively recent times they have not changed much iu their organization. And further, I doubt very much that we will ever meet among the more recent forms of existing types of reptiles any that will show in their morphology 1 These were first used, by the author quoted, in a paper entitled " O n the Characteristics of the Primary Groups of the Class Mammals," Proc. A m . Assoc. Adv. Sci. vol. xx. p. 291. |