422 



KANSAS UNIVERSITY SCIENCE BULLETIN. 



KEY TO SPECIES IN UNITED STATES. (BROWN.) 



Postnasal in contact with preocular; the light line to angle of mouth begins at 

 nostril S. catenalus. 



Postnasal separated from preocular by loreal ; light line to angle of mouth begins 

 at the eye S. rniliarius. 



Sistrurus catenatus Garman. 



Prairie Rattlesnake or Massasauga. 

 Caudisona tergeminus Wagler, Nat. Syst. Amph., p. 176. 

 Crotalus tergeminus Say, Long's Esped. Rocky Mts., I, p. 499. 

 Sistrurus catenatus Garman, N. Amer. Rept., 1883, p. 118. 



Fig. 37. 

 Sistrurus catenatus (iarm. 



Rows of scales 23-25 ; outer row not keeled, second row 

 keeled only at the base or not at all. Outer margin of the 

 occipitals rounded. Occipitals broad posteriorly, narrow ante- 

 riorly. Considerable variation appears in these plates. In 

 some specimens they are narrower posteriorly than anteriorly 

 and lose their rounded outline. Frontal triangular with gently 

 convex margins, in the type specimen. This plate also presents 

 many variations. In a specimen now before me it is regularly 

 pentagonal. Frequently it is truncated at the apex and the 

 separated part remains as an extra plate. Superciliaries large, 

 broad in the middle and narrow at the ends. Prefrontals with 

 only one sharp angle ; the outer margin rounded. Internasals 

 triangular, anterior margin convex, posterior margin concave. 

 Rostral high and narrow, broadest near the lower edge. 

 Two nasals, anterior rectangular, narrow and high ; posterior 

 almost triangular. Nostril very small. Preoculars long and 

 irregular, the upper reaching nearly to the internasal. Loreal 

 small and irregular in shape. Superior labials 10-12. Inferior 



