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BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



and parietals are paired; prefrontals two in the three forms of the 

 deppei group (fig. 5), four in all other forms of the genus (figs. 2-4); 

 loreal usually present in some forms, only occasionally in others; 

 nasals paired on either side, with the external nares between them; 

 preoculars normally 1 or 2, occasionally 3; postoculars normally 2 in 

 deppei and lineaticollis, normally 3 or 4 in all other forms of the 



Figure I.— The normal arrangement of head scales in Pituophis: A, From above; B, from the side, az, 

 Azygos; fr, frontal; il, infralabial; in, internasal; to, loreal; na, nasal; pa, parietal; pf, prefrontal; po, post- 

 ocular; pr, preocular; ro, rostral; si, supralabial; so, supraocular. 



genus, occasionally 2, 5, or 6; azygos between frontal and prefrontals 

 always absent in some forms, present or absent in others; azygos 

 between prefrontal and preocular on either side, or between other 

 head scales, occasionally present; supralabials 8 or 9 normally, most 

 often 9 in vertebralis, most often 8 in all other forms, occasionally 7 

 or 10; infralabials 10 to 15, usually 14 in mugitus and ruthveni, most 

 often 11 in deppei, normally 12 or 13 in all other forms; a single men- 



