186 M. Von Summering on tlte [Sept. 



tribe, it is principally the fore part of the head that charac- 

 terizes the varieties occurring among them, as in the hinder part 

 the general resemblance is less diversified. 



It is owing to this striking difference in the face that we can 

 distinguish at first sight the head of the gavial from that of the 

 crocodile, and these again from those of the gecko, the iguan, 

 the stellio, and the draco; not only in a fresh and unprepared 

 state, but still more plainly in the skeleton. Thus it is princi- 

 pally in the parts forming the face that we perceive the most 

 decided difference between the scull of the lacerta monitor, tupi- 

 nambis, draco, and stellio. Similar differences in these parts 

 are to be discerned in Camper's admirable plates of the sculls of 

 the tupinambis, tequixin, and iguan.* 



Since, therefore, it is the jacies that principally shows the 

 resemblance, or the difference between the various species of 

 lizards ; and as fortunately the greater part of this is here pre- 

 served so as to be plainly distinguishable ; for whatever imper- 

 fection there happens to be on one side is supplied by the exist- 

 ence of the corresponding parts on the other side, it becomes 

 less difficult for us to compare these lacerta of the former world 

 with those of the present one. 



Among all the varieties with which 1 am acquainted, I find 

 that, except with regard to size, the fades of our lacerta 

 bears the greatest resemblance to that of the lacerta monitor. 

 This resemblance is most obvious on the left side (PL VIII f), 

 fio\ 2, where, on comparing them, we find an evident analogy in 

 the general conical form of the upper jaw ; the hollow of the eye 

 equally large in proportion ; an equally large cheekbone ; 

 the same furrow, or slight hollow, between the bones of the nose, 

 and a similarly shaped under jaw. 



Judging from the scull of a lacerta monitor now before me, and 

 likewise from the plate of an iguan by Fischer,;}; or that of a large 

 .teguixin by Camper,§ I am of opinion that not only the entire 

 intermaxillary bone is wanting, but also a portion of the right 

 and left upper jaw. This part, which is also deficient in most of 

 the plates of the Maestricht animal, as well as the incisores teeth 

 belonging to it, can be restored from the representation given by 

 Camper, || who possesses a natural specimen. 



Teeth. 



If the teeth in our animal be compared with those of the 

 lacerta monitor, a striking difference will be evident ; for 

 although the manner in which they are fixed into the jaw, and 

 also that of their arrangement appear to be similar, their form 



* Annales du Museum, a Paris, torn. xix. PI. 11, fig. 5, 6, 8, fig. B, fig. C. 

 + This Plate has been reduced. — Ed. 



j On the different Forms of the intermaxillary Bones of Animals, Leipsig, 1 800, 

 tab. iii. fig. 8. 



§ Annales du Museum d'Hist. Nat. a Paris, torn. xix. 1S12, PL 11. fig. 8. 

 |1 Ibid. fig. 3. 



