AMPHIBIA AND EEPTILIA OF COLORADO 93 



twenty feet or more and is terrifying enough to the person unfamiliar 

 with this type of snake. The Bull Snakes are oviparous and lay eggs 

 almost as large as hen's eggs. They range over the United States and 

 Mexico. Their food consists largely of small mammals and birds. 

 Because of the large number of rodents eaten by these snakes they are 

 to be regarded as not only harmless snakes, but as beneficial snakes. 



Pityophis catenifer (Blainville) 



Bull Snake {Figures 24, 25, 26, 35 and 36) 

 Coluber catenifer Blainville, Nouv. Ann. du Mus., Vol. IV, p. 290, 1835. 



Three subspecies of this snake are recognized, two of which occur 

 in Colorado. These are distinguished particularly by their range and 

 less exactly by the size of the rostral plate. 



a. Range, Canada to northern Mexico, west of the Mississippi River and east 

 of the Rocky Mountains; rostral plate separating the internasal plates for 



two-thirds or more of their length P. c. sayi (Schlegel). 



aa. Range, west of the Rocky Mountains. 



b. Range, Great Basin from Utah and Nevada south to Arizona and New 

 Mexico, east to Colorado and west to the Sierra Nevada Mountains; 

 rostral plate separating the internasal plates for not more than one- 

 third of their length. . . . P. c. bellona (Baird and Girard). 

 bb. Range, west of the Sierra Nevada Mountains; rostral plate just reach- 

 ing the internasals P. c. catenifer (Blainville). 



Pityophis catenifer sayi (Schlegel) 



Coluber sayi Schlegel, Ess. Physionomie des Serpentes, p. 157, 1837. 



Pityophis catenifer sayi Brown, Proc. Acad. Nat. Set. Phila., Vol. LIII, p. 55 

 1 001. 



Pityophis elegans — Yarrow, U.S.N.M. Bull. 24, p. 108, 1882 (between the 

 Arkansas and Cimarron, N.Mex.). 



Pityophis sayi sayi — Yarrow, U.S.N.M. Bull. 24, p. 105, 1882 (Pagosa, Colo.) ; 

 Cary, N. Am. Fauna, No. 33, p. 27, 1911 (eight miles west of Naturita, Colo.). 



Dorsal scales keeled, excepting the first three or four rows on each 

 side (sometimes as many as n rows are smooth on each side), in 27 

 to 35 rows; superior labials, 8 or 9; inferior labials, 12; postoculars, 

 3 to 5; nasal opening large and prominent, directed posteriorly; 

 rostral plate large and recurved; ventrals, 200 to 250; tail less than 



