212 BULLETIN 154, UNITED STATES NATIONAL MUSEUM 



Coloration distinctive; under surfaces usually sullused with much 

 blackish; gular region usually slate or smoky; all caudal surfaces 

 brownish, chocolate, or black, usually darker below; base of tail 

 sometimes with light spots laterally, tip dark, blackish; back and 

 upper surfaces of hind legs with numerous small white spots which 

 are ver}" abruptly defined against the general ground color; spots 

 smallest dorsally, largest laterally ; sides onlj'- slightly suffused with 

 deep black and with occasional white flecks at the ventro-lateral 

 line; spots or indications of spots absent in the region above the 

 level of the tympanum and anterior to the insertion of the forearms. 



The femoral pores are often very hard to count because of the 

 black suffusion which usually covers the under surface of the hind 

 limbs. 



In young si)ecimens, the characteristic white spots are more 

 numerous and better defined, but unlike those of catalinensls of the 

 same age, they do not extend above the level of the tympanum, for- 

 ward of the insertion of the forearm. On the sides of the neck, how- 

 ever, a few small spots may be seen. In all individuals there is an 

 evident tendency for the spots to disappear anteriorly with age, and 

 in no large specimens are spots present anteior to the forearms. 

 This ontogenetic loss of spots progresses more rapidly along the 

 middorsal line than at the sides. 



Only 12 specimens of this species have been available for examina- 

 tion. Their measurements have been summarized as follows : Body, 

 46-75 mm.; tail, 105-200; total length, 155-275; length of tail as 

 l^ercentage of total length, 65.5-73.0; width of head, 7-10; width of 

 head as percentage of body length, 13.7-16.0; hind leg, 32-50; length, 

 of hind leg as percentage of body length, 61.5-74.2; head scales 

 uniform as indicated above. 



Rmige. — This spotted Avhiptail is confined to San Pedro Nolasco 

 Island in the Gulf of California (Van Denburgh and Slevin, 1921«, 

 p. 97, C.A.S.). 



Habitat and habits. — According to Van Denburgh (1922, p. 546), 

 " this beautiful lizard was not common in its natural habitat. Most 

 of the specimens were found (by Mr. Slevin) around tlie nests of a 

 colony of brown pelicans, where they were seen catching flies and the 

 numerous insects attracted by dead fish and other refuse. A few 

 Avere found among the fallen cacti in the deep gullies which run down 

 to the sea coast." 



San Pedro Nolasco Island is only 214 miles long by three-fourths 

 of a mile wide. It is but a short distance (less than 10 miles) from 

 the mainland of Mexico. Its shores rise abruf)tly at most points to 

 almost 500 feet and the highest elevation is said to be 1,071 feet. 

 The island itself is a barren, rocky mass of volcanic origin. 



