186 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 138, No. 9 
fifth toe and extremity of fourth exceeds the distance between end of snout 
and posterior border of ear; 15 femoral pores on each side; tail distinctly com- 
pressed; caudal scales larger than dorsals, strongly keeled and mucronate 
except those on basal third underneath, which are smooth; males with slightly 
developed post-anal scales. 
Coloration (in aleohol).—Bronze-colored above; a broad, dark stripe along 
each side with a light area above; a black vertical bar in front of the shoulder; 
head reddish brown spotted with darker; lips with dark vertical bars; a very 
noticeable black spot encircled with a ring of light yellow on the posterior 
margin of the parietal shield, not involving the ‘‘pineal eye’’; throat with 
oblique bluish bands converging posteriorly; breast yellowish; sides of belly 
pale green, broadly edged with blackish blue near the median ventral line. 
Dimensions. —Snout to vent, 56 mm.; shielded portion of head, 13 mm.; 
snout to ear, 14 mm.; length of fourth toe, 15 mm. 
Remarks.—Although the new species resembles Sceloporus pyrocephalus 
Cope in many of its characters, there are several striking differences which 
will enable the two species to be distinguished immediately. The black spot 
on the parietal shield, which in S. pyrocephalus encircles the ‘‘pineal eye,” 
in S. nelsoni is on the extreme posterior border of the parietal, not involving 
the pineal eye, and is itself encircled by a ring of light color which becomes 
slightly darker just anterior to the black spot. The snout is quite flat in 
S. pyrocephalus; one row of regular scales separates the supraoculars and the 
supraciliaries. In the new species the frontal ridges are fairly prominent; 
there are two irregular rows of small scales separating supraoculars and 
supraciliaries; the dorsal scales are larger and more spiny, and the femoral 
pores are more numerous. The ventral coloration of the two species is 
entirely different—in the males of S. pyrocephalus there is a startling black 
and white herring-bone pattern of convergent stripes, while in the S. nelsoni 
the pale blue areas on the sides are simply edged with black, as in the large 
majority of the Scelopor. 
In addition to the type, there are 10 specimens in the National Museum, 
five from near Mazatlan, one from Culiacan, three from Rosario and one from 
Barranca Ibarra. The coloration is constant, except that the specimens from 
near Mazatlan are somewhat lighter. The femoral pores vary in number 
between 15 and 20. ; 
The new species is named in honor of Dr. E. W. Nelson, Chief of the Bio- 
logical Survey. 
