REPTILIA: VARANOSAURUS 91 



closely united with the maxillae that the character and number 

 of the teeth cannot be made out. 



Varanosaurus acutirostris Broili, so far as the skull and skeletal 

 characters are determinable from the figures and descriptions by 

 the author in the incomplete condition of the type specimen, agrees 

 well with the present species, save in the skull proportions and the 

 teeth. As seen in the figure, the skull of V. acutirostris is 

 more elongated and slender, the length in front of the orbits being 

 equal to three times the diameter of the orbits, the orbits situated 

 back of the middle of the skull. In the present species the length 

 in front is scarcely more than twice the diameter of the orbit, 

 and the orbits are in front of the middle of the skull. Furthermore, 

 there is no large tooth in the position of the mandibular tooth of the 

 present species, the enlarged tooth of V. acutirostris being much 

 farther forward. Furthermore, and more important, Broili gives 

 fifty-four as the whole number of teeth in the upper jaws of this 

 species, while there are not more than thirty-four in V. brevirostris. 

 Notwithstanding these differences, so great is the general resem- 

 blance between the two that I have been reluctant to admit the dis- 

 tinction of our species. But such differences cannot possibly be 

 due to either age or individual variation. I have therefore given 

 to the present species the name Varanosaurus brevirostris. 



In the phylogeny of the reptilia we have assumed a high degree 

 of importance for the different structural variations of the temporal 

 region; and, in general, I believe that this assumption is justified. 

 We recognize at least three and perhaps four chief types of reptiles, 

 four chief phyla perhaps, as based upon the structure of this region: 

 The cotylosaurian or stegocrotaphic type, in which the temporal 

 region is wholly arched over; the double-arched or saurocrotaphic 

 type, as I have called it, in which there are two temporal vacuities, 

 the upper one bounded below by the union of the squamosal and 

 postorbital, the lower by the jugal and quadrato jugal ; and the 

 single-arched or therocrotaphic type, in which the single vacuity 

 is bounded below by the jugal and quadrato jugal; and perhaps 

 a fourth type in which the upper arch and vacuity alone are present, 

 bounded by the squamosal and postorbital below. But I do not 

 feel so certain as to the distinction between these two latter types. 



