52 PROCEEDINGS OF THE ACADEMY OF [Jan., 



PITYOPHIS llolljrook. 



Pituophis Holb., No. Am. Herp., IV, 7 (1842); B. and G., I c, 64; 

 Cope, I. c, 638, and Eep. Nat. Miis., 865 ; Coluber (part) Boul., I. c, 

 II, 24. 



]Maxillary teeth smooth, equal; rostral exteuded behind; one 

 loreal; one preocular with sometimes a small one beneath; tAvo 

 nasals; two internasals; four to six prefrontals; scales keeled with 

 pits in 29-35 rows; anal entire; size large; head moderately 

 distinct. 



Hab. — North America and Mexico. 



The species of Pityo])his within the United States may be deter- 

 mined upon the following grounds: P. melanohucus, from the 

 eastern States, has a high rostral, in most cases reaching the pre- 

 frontals, and has large dorsal spots, 26-35 in number, on the body ; 

 usually about the four outer rows of scales are smooth. 



P. sayi, from west of the Mississippi to the Rocky Mountains, 

 has the rostral less high, usually reaching about two-thirds of the 

 distance to the prefrontals, and has smaller spots, 40-60, on the 

 body, and usually seven or eight smooth rows of scales. 



P. catenifer, from the Pacific coast, west of the Sierra Nevada, 

 has a low rostral, usually not penetrating between the internasals, 

 and agrees generally in pattern with sayi. 



These characters of the rostral and the dorsal spots are fairly 

 constant, but examination of a considerable number of specimens 

 from the region of the Great Basin leaves no doubt in my mind 

 that the form found there intergrades with both catenifer and sayi, 

 and reduces them to subspecies. The two species recognized here 

 may in almost every case be distinguished by color characters 

 alone : 



Rostral high; no head bands; spots large and few, 



1. P. melanoleucus. 

 Rostral lower; head bands distinct; spots small and many, 



2. P. catenifer. 



Pityophis catenifer Blainville. 



Coluber catenifer BL, Nouv. Ann. du Mus., IV, 290, PI. 21, fig. 2 

 (1835). 



In this species the rostral varies from low and broad to high and 

 narrow above, penetrating sometimes between the internasals but 

 not reaching the prefrontals; prefrontals usually four, but occa- 



