408 REPORT OF NATIONAL MUSEUM, 1898. 



II. Ono large subrictal projectiug jilate; temporal row of couic, plates continued to 

 below orbit; dorsal scales witbout basal I'osette. Femoral pores on borders of 

 scuta. Two occipital horns P. coronatum; P. cerroense; P. hIainviUei. 



III. No subrictal prominent scale; temporal row not continued to below orbit; four 

 occipital horns; large dorsal scales generally without rosette; femoral pores in 

 interior of scuta P. solare. 



IV. No subrictal prominent scale; temporal cones not continued to below orbit; 

 large dorsal scales with basal rosette; one occipital horn; femoral pores at mar- 

 gins of scuta /'. cornutum; P. asio; P. taurus. 



The attempt lias been made to define more than one genus from the 

 characters presented by the above species. One of the characters 

 viewed as indicating this result is the varying position of the nostrils 

 as regards the canthus rostralis. On this basis the P. coronatum 

 might be as readily referred to one division as the other, as it is in this 

 respect exactly intermediate. Such a division would violate the affini- 

 ties expressed in the second table. This is, however, not an insuperable 

 objection, as allied genera not infrequently possess parallel series of 

 species. 



The largest species is the southwest Mexican P. asio. It is remark- 

 able for the reduction of its temporal horns to two on each side, and 

 the large size of its superciliary horns, which equal the posterior tem- 

 poral and occipital in length. The P. taurus, from southeastern Mexico, 

 is remarkable for the presence of only one temporal spine, which is 

 very large, and the abortion of all the other spines, of which the occip- 

 ital are represented by rudiments. Eleven species are known, three 

 being restricted to the tropical parts of Mexico, namely, P. asio, P. 

 taiirus, and P. hraconnierii. 



Habits. — Under the head of Phrynosoma doufflassii, Dr. Stejneger' 

 thus writes of the metachrosis, which is so observable in this genus: 



Much has been written in regard to the perfection with which these animals 

 "imitate" the color of the ground on which they live, and our own observations 

 fully verilied the statement that they afford one of the most striking examples of 

 protective mimicry. 



In the cedar and pine belts of the San Francisco Mountain the dark color of the 

 soil and stones covering the surface is closely matched by the ground color of the 

 Phrynosomas, while the greenish gray and orange colored markings, which some- 

 what irregularly adorn their backs, are perfect imitations of the lichens covering the 

 rocks and pebbles among which these odd-looking creatures live. Near the rim of 

 the Grand Canyon of the Colorado, on the other hand, the ground is covered with 

 small pebbles of variously colored sandstone, ranging from a clayey white to brick 

 red and dark brown, and the specimen which I collected there (No. 15721) is such a 

 faithful reproduction of the surroundings that it would undoubtedly have remained 

 undetected had it not been moving. Even more remarkable are the specimens which 

 Dr. Merriam collected in the black lava belt, east and northeast of the mountain. 

 One of these (No. 15815) was brought to camp aliv(^, enabling me to make the fol- 

 lowing description of the fresh colors: "Ground color of upper side, including head, 

 satiny black; light markings on median third of body dull 'Naples yellow,' abruptly 

 changing into the yellow ocher of those on the sides; tips of most lateral spines 



'North American Fauna, No. 3, 1890, p. 114. 



