(4) _C. durissus_ (Common Rattle-Snake).--7 or 8 longitudinal series of scales between the supraoculars, 3 or 4 series of scales between the eye and the labials; 13-16 supralabials; scales in 25-29 rows, dorsals strongly keeled; ventrals 169-181; 24-32 subcaudals. [Illustartion: FIG. 74.--_Crotalus scutulatus_ (Texas Rattle-Snake). (After Baird and Stejneger.)] Colour pale greyish or brownish, with a dorsal series of large blackish rhomboidal spots; a yellowish cross-line between the eyes; snout blackish; end of tail usually black; belly yellowish, more or less spotted with brown or black. Total length may be as much as 8 feet (2,400 millimetres). _Habitat_: South-eastern United States, from North Carolina to Florida and the mouths of the Mississippi. (5) _C. horridus._--Supraoculars considerably narrower than the space between them, which is covered by 3-8 longitudinal series of small scales; 12-16 supralabials; body scales in 23-29 rows, dorsals very strongly keeled; 165-178 ventrals; 19-29 subcaudals. Colour greyish-brown, usually with a rusty vertebral stripe, and =V-= or =M-=shaped blackish cross-bands; head uniform above, with a dark band from the eye to the angle of the mouth; usually a pair of roundish or triangular dark spots on the nape; belly yellowish, uniform or spotted with blackish; end of tail blackish. Total length, 1,340 millimetres; tail 135. _Habitat_: United States, from Massachusetts and Iowa to Northern Florida and Texas. (6) _C. tigris._--13-15 supralabials; scales in 23 or 25 rows, dorsals strongly keeled; 166-181 ventrals; 26-46 subcaudals. Colour yellowish or pale brown, with a dorsal series of brown spots and cross-bands posteriorly; sides with smaller dark spots; belly yellowish, spotted with brown. Total length, 380 millimetres; tail 50. _Habitat_: Southern California, Lower California, Nevada, Colorado, Arizona, and Northern Mexico. (7) _C. mitchelli._--14-16 supralabials; scales in 25 rows, striated, dorsals strongly keeled; 178-198 ventrals; 24-26 subcaudals. [Illustration: FIG. 75.--_Crotalus confluentus_ (Pacific or Mottled Rattle-Snake). (After Baird and Stejneger.)] Colour greyish-yellow to salmon-red, finely punctulated with brown, with a dorsal series of transverse darker spots; belly yellowish. Total length, 1,020 millimetres; tail 90. _Habitat_: Desert regions of Southern California, Lower California, and Arizona. (8) _C. triseriatus._--9-13 supralabials; scales in 21-25 rows, dorsals strongly keeled; 142-184 ventrals; 22-30 subcaudals. Colour olive or brown, with a vertebral series of rather small dark brown spots edged with black and white; belly yellowish, spotted with dark brown, or dark grey-brown powdered with whitish. Total length, 530 millimetres; tail 55. _Habitat_: Mexico. (9) _C. polystictus._--Closely allied to the foregoing, but 4 internasals, 14 or 15 supralabials, and scales in 27-30 rows; 123-151 ventrals; 18-23 subcaudals.