CROTALUS. 7 



Head very broad anteriorly, outline little tapering. Head above 

 covered with many small tuberculiforra scales, showing a substelli- 

 form radiation. Interval between superciliary plates filled with small 

 scales, nearly uniform in size ; row bordering the superciliaries verj' 

 small. Scales in front of the superciliaries variable : in one speci- 

 men there are two rows of four each, of considerable size ; in another 

 they are larger than the rest, but irregular. Scales on the cheeks 

 large, flat, smooth. 



Ground-color, light brown above. Along the back a series of 

 subhexagonal or octagonal blotches, formed by a skeleton of dull 

 yellowish, constituting a dorsal chain. The space thus enclosed of 

 the ground-color is margined faintly with dark brown : the width 

 of the interval between the successive blotches is from one-half to 

 one and a half scales. These spots are frequently confluent, two and 

 three running together. Where most distinct the spots are four scales 

 long and eleven wide. On each side of this dorsal series is a second, 

 separated by a single row of scales, the blotches extending from the 

 abdominal scutellse to the 5th or Gth row. These are smaller than 

 the dorsal, and subcircular. Opposite the transverse light bands, 

 and in the open space between four contiguous blotches ou the sides, 

 smaller blotches arc indistinctly visible. Posteriorly, the spots on 

 the back and sides are confluent and darker; in one specimen form- 

 ing 17 half rings, encircling the back, leaving about 24 dorsal 

 blotches. Abdomen greenish yellow, more or less clouded with 

 brown at the bases of the scales. Head dark brown ; a light line 

 from posterior portion of the superciliaries along the 4th row of su- 

 pralabial scales back to the angle of the jaws, on the occiput, where 

 it expands into the color of the under part. Upper labials of the 

 same light color behind, rapidly widening anteriorly so as to include 

 whole front and side of the face, leaving only the top of the head 

 dark. The space about the facial pit darker. 



The theory of coloration is that of decussating lines, which, when 

 they intersect, unite so as to have the angles of intersection truncated. 



The species has a general resemblance to C. atrox in the arrange- 

 ment of the blotches, but is darker, and has about 17 dark half rings 

 posteriorly instead of 4 or 5. In G. atrox the head is narrower and 

 more triangular, the space between the superciliaries narrow, and 

 occupied by angulated larger scales instead of small tuberculous ones. 

 In C. atrox, the row bordering the superciliaries is much larger than 

 the rest, and the scales on the top of the head generally more angu- 



