1852.] 127 



lar, very thin, without carinae and finely denticulated posteriorly. On the sides, 

 the upper part of the legs and on the tail, the scales taper posteriorly into a sharp 

 point. The plates on the upper surface of the head are rather small and irregu- 

 lar in shape, except the occipital, which is larger than in any other allied species. 

 The general color is olivaceous, reddish on the back and sides, with transverse 

 dorsal black bands, much broaSer and more distinct on the tail. There is also a 

 black collar convex backwards, embracing the region of the neck above and 

 terminating in advance of the origin of the fore legs. 



At the request of Col. J. D. Graham, we have dedicated this species to the 

 memory of the late Hon. Joel R, Poinsett, whose name is associated with the 

 progress of science and the useful arts throughout his public career, especially 

 while Secretary of War of the United States. 



Localities. Rio San Pedro of the Rio Grande del Norte, and the province of 

 Sonora. 



ScELopoRus Clarkii, B. and G. Allied to bothSc. torquatus^n^Sc. spinosus, 

 it resembles the former in the presence of an imperfect black collar, which is 

 more distinct in the young. This, however, is never seen to form a complete 

 crescent on the neck, but is gradually diminishing in width from its origin in 

 advance of the fore legs towards the upper part of the body. From Sc. spinosus 

 it differs by having proportionally much larger scales on the temporal region, and 

 all the scales terminated by a much less developed posterior point. The body is 

 uniform yellowish green, excepting the band of black on the sides of the head. 

 The male has a bluish abdomen, indistinctly black along the middle region. The 

 lower surface of the head is blue, on the middle region surrounded with black. 



Dedicated to John H. Clark, to whose skill as a collector, and untiring zeal for 

 science, the world is indebted for the splendid zoological collections sent and 

 brought home by Col. Graham from the survey of the Mexican boundary. 



Locality. Province of Sonora. 



ScELOPORus Thayerii, B. and G. This species has the general appearance of 

 Se. scalaris and Sc. graciosus. It differs from both by a very readily apprecia- 

 ble character, which consists in the possession of much larger scales on the upper 

 region of the body. The color is yellowish green above, with two longitudinal 

 bands of brown or black, and two yellow ones, on each side. Sometimes, instead 

 of bands, a series of small patches of the same color is observed, the black 

 patches also form transverse and undulating narrow bands. The belly is uniform 

 yellow underneath, the male has on each side an elongated patch of blue, with a 

 narrow band of black along the abdominal margin. Under the throat there is a 

 medial black patch, limiting on each side another blue spot. 



At the request of Col. Graham likewise, we have dedicated this species to Col. 

 Sylvanus Thayer, of the U. S. Engineer corps, and the founder of the present 

 system of instruction at the U. S. Military Academy at West Point, as a tribute 

 to the high scientific attainments and valuable services in his profession as an 

 officer. 



Localities. Indianola, on the Gulf of Mexico, San Antonio, (Texas,) El Paso 

 del Norte, and as far westward as the province of Sonora. 



ScELOPORus DisPAR, B. and G. No species of the genus Sceloporus will be 

 more easily recognizable than the present one, on account of the great disparity 

 which exists between the scales on the upper part of the body and those on the 

 tail, the latter being twice as large and more strongly carinate-d. The scales on 

 the abdomen are likewise a little larger than those on the back. The color in the 

 only specimen which we have hitherto seen of this species is uniform blackish 

 green, but as it has been collected for a long time, the color may have changed 

 considerably. The head is reddish brown. The abdomen in the male is blue 

 from the fore to the hind legs, leaving a medial narrow space of the color of the 

 throat and thighs, and along which a narrow black band separates it from the 

 blue. 



Locality. Vera Cruz. Sent by Dr. Burroughs to the Academy of Natural 

 Scinces of Philadelphia, where the specimen described is preserved. 



