Orbicular Lizards, or Horned Agamas. 383 



bases anterior, forming the outer border, which projects slightly be- 

 yond the general border, and is bluntly serrated in the middle, and 

 with a dental process at the basal angles: — of the twelve plates 

 composing the sternum, all are of different shape and size, the cen- 

 tral longitudinal suture irregularly curved. 



Head of moderate size, rather depressed ; the upper jaw armed 

 at its apex with two strong dental processes : — color of the crown 

 of the same dark olive, mottled with black and yellow, as the rest 

 of the animal — throat and neck with bright yellow longitudinal lines, 

 which extend on the fore feet : — the inferior surfaces of the mar- 

 ginal plates marked with black bands striped with yellow. 



Tail of the ordinary dimensions of animals of this genus ; — the 

 same may be observed respecting the feet ; the anterior nails are 

 longer than the hind nails; in both, the middle nails are the longest. 



Dimensions. — Length of the back plate 8 inches ; breadth of the 

 same 6 in. : length of the sternum 7 in. ; breadth of the same 4 in. : 

 depth of the animal 2 in. 2 tenths : length of the head 2i in. ; 

 breadth of the same 1 in. 1 tenth : length of the longest claw 6 

 tenths ; length of the longest posterior claw 4 tenths. 



General Remarks. — My friend Thomas Nuttall, whose indefati- 

 gable exertions in natural history have extended throughout North 

 America, on his recent travels across the continent to the Pacific 

 Ocean, obtained the present specimen in the fresh water ponds in 

 the vicinity of the Oregon or Columbia River, where this species 

 was observed to abound, to the exclusion, according to his observa- 

 tion, of any other tortoise. 



Art. XXIII. — Notice of the Orbicular Lizards, or horned 

 Agamas; by R. Harlan, M. D., &,c. 



Among the valuable treasures in natural history, recently brought 

 by Mr. Nuttall from his journey across the Rocky Mountains to the 

 Pacific Ocean, are several excellently preserved specimens of a large 

 species of Orbicular lizard, which he kindly placed at my disposal 

 for the purpose of description. Mr. Nuttall obtained his specimens 

 in. California, and preserved them living for many weeks : he con- 

 sidered them of a very docile nature, never attempting to use their 

 horns in self-defence ; they inhabit under stones, and in holes, in the 



