Total length, 680 millimetres; tail 80.
Habitat: Great Lakes district; United States east of the Rocky Mountains and west of the Mississippi; Northern Mexico.
(3) S. ravus.—11 or 12 supralabials; scales in 21 or 23 rows; 147 ventrals; 26 subcaudals.
Colour yellowish-brown, with a dorsal series of dark brown spots, longer than broad, and a series of transverse dark bars on each side; belly yellowish, spotted with blackish-brown.
Fig. 71.—Sistrurus catenatus (Prairie Rattle-Snake, or Massasanga). (After Holbrook and Stejneger.)
Total length, 200 millimetres; tail 22.
Habitat: Vera Cruz, Mexico.
(d) Crotalus (Rattle-Snakes).
These snakes differ from all others in that the end of the tail bears a series of large conical scales, forming rattles, each fitting into the next and movable in such a manner that when the reptile causes them to move they produce a strident sound ([fig. 72]).