234 DR. R. W. SHXJFELDT ON [Apr. 1, 



skeleton of a Helodennu. 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 ail that I have seen in the works of other authoi's, 1 am 

 strongly inclined to believe that when the morphology of such species 

 that are now grouped in the genera Xantusia, Xenvsaurus, and 

 Lepidophyma is thoroughly worked out, no inconsiderable amount of 

 light will be thrown upon the subject of the affinities of the Heloder- 

 tnatidce. 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 pre- 

 sented 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 18/2 introduced the use of Superfamilies ^ ; and they 

 have been steadily growing in favour with naturalists ever since. The 

 same zoologist has already created a superfamily to contain the 

 HeloJerms. This he has termed the Uelodermatoidea, and has 

 selected the following characters to designate it, viz.: — " Eriglossate 

 Sauiians with concavo-convex vertebrae ; claAacles undilated prox- 

 imally, and post-orbital bony arches, but without post- frontosquamosal 

 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 hut 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 Helodermatidce, 

 inclined me to beheve that these reptiles are probably derived from a 

 rather old stock, and that during comparatively recent times they 

 liave not changed much in 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 



' These were first iised, by the author quoted, in a paper entitled "On the 

 Characteristics of the Priuiarj* Groups ol' the Class Mammals," Proc. Am. Assoc. 

 Adv. Sci. vol. XX. p. 291. 



