LIVING m THE SOCIETY'S MENAGERIE. 219 



has rarely been left without one or two individuals of this rare species. The typical 

 specimen is stated to have been obtained at San Domingo ; but of none of the speci- 

 mens received by the Society is the exact origin known ^. 



The description given by Dumeril and Bibron applies to our specimens in every par- 

 ticular, except in the following points. The teeth cannot be described as " tricuspid ;" 

 the central main cusp is free from denticulation, and two or three small notches indent 

 the margin at some distance from the point of the tooth ; towards the front the teeth 

 are simply conical. The teeth are larger than in Iguana tuberculata, twenty in each 

 maxillary, six in the single intermaxillary, and twenty-two in each mandible. In the 

 scutulation of the upperside of the head I observe that there are three pairs of scutes 

 interposed between the nostril and frontal horn, the posterior and middle being conically 

 raised. The nasal shield forms a direct suture with the rostral, without any intervening 

 accessory scutes, as described by Dumeril. 



The skeleton is very similar to that of Iguana {tuberculata). The vertebrae are more 

 slender and depressed, and provided with much shorter and more feeble neural spines ; 

 but their number is the same in both species, viz. six cervical, eighteen dorsal, and two 

 sacral. Also the skull (PI. XLIV.) is built entirely upon the plan of Iguana ; but it is 

 more massive and depressed, with a prolonged rostral region. The zygomatic arch is very 

 broad ; the parietals are horizontally spread out, not vertically as in Iguana, forming a 

 broad roof over the occipital region. Again the fore part of the skull shows much firmer 

 and more solid ossifications than in Iguana, the floor of the long oval nasal cavity being 

 nearly entirely osseous. The posterior process of the articular of the mandible is 

 short, and much more obtuse than in Iguana. 



The bones of the limbs do not show any noteworthy difference from those oilguajia ; 

 but they are throughout shorter. The following are the measurements taken from 

 skeletons of Metopoceros and Iguana tuberculata which are of the same size, the 

 vertebral column to the first caudal vertebra measuring 10 inches. 



Iguana. Metopoceros. 



miUim. millim. 



Humerus 60 52 



Ulna 51 48 



First metacarpal 12 12 



First finger, first phalanx 11 . . . ' . . 9 



Second metacarpal • . . 16 14 



Second finger, first phalanx 10 8 



Second finger, second phalanx .... 11 8 



Third metacarpal 19 17 



Third finger, first phalanx 10 8 



Third finger, second phalanx 10 7 



Third finger, third phalanx 12 7 



' List of the Vertebrated Animak, 7th ed. p. 499. 



