CROCODILIANS, LIZARDS, AND SNAKES. 789 



series, with two apical fossa\ Subcaudal scutelhi' in two series; anal 

 plate divided. Two preoculars; loreal present; two nasal plates. 

 Form elongate. 



The species of this genus are elongate in form and active in move- 

 ment, so that the j)opular names of "whip-snake" and "racer" are 

 apprdpriate. Although at home on the ground they climb bushes and 

 low ti ees, rarely ascending to any great lieight. They are skillful in 

 cai)tiiring young birds, as well as small mammals and reptiles. They are 

 distributed over all North America south of the boreal region, and are rep- 

 resented, like most of our other genera of snakes, by a greater multiplic- 

 ity of forms in the southwestern section of the continent. One species 

 inhabits Mexico exclusively. The species are distinguished as follows: 



I. Scales in seventeeu rows; superior labials seven. (Frontal plate nearly as wide 

 as superciliaries posteriorly; muzzle rather produced; colors not in stripes.) 

 Two labials bounding orbit below; form robust; colors generally nniforni, 



always so on lips and throat Z. constrictor Linnanis. 



One labial bounding orbit below; form more slender; more or less spotted on 



the lips and throat Z.mentorarins Dunioril and Bibron. 



II. Superior labials eight ; scales in seventeeu rows. ( Frontal as wide posteriorly as 

 superciliary at same point; loreal longer than deep.) 

 Rostral plate little prominent; frontal with straight sides not touching pre- 

 frontals; loreal subdivided; oiive above, yellow below. 



Z. stcjnef/erianus Cope. 



Rostral plate prominent; frontal with concave sides in contact with preoculars; 



loreal entire; light brown above, pale leaden below Z. conirostris Cope. 



III. Scales in nineteen rows; superior labials eight. (Frontal plate one-half as 



wide as superciliary behind; muzzle narrowed, produced.) 

 Slender; above black; below yellow Z.jiageUum piceiis Cope. 



IV. Scales in seventeen rows; superior labials eight. (Fi'ontal plate one-half 



width of superciliaries posteriorly; form slender.) 



Muzzle narrowed, more or less decurved; without or with dark shade or cross- 

 spots anteriorly ; young cross-spotted Z. far/eUnm Catesby. 



Muzzle narrowed; ])ale with a latei'al brown stripe anteriorly; young striped; 

 no temporal spot Z. aemiihicatus Cojte. 



Muzzle flattened, wider; a yellow stripe on third and fourth rows of scales only ; 

 dorsal scales brown ; a yellow temporal spot; belly yellow; lateral stripe con- 

 tinuous to origin of tail; throat and upper and lower labials spotted; posterior 

 upi)er labials less elongate Z. laieraliif Hallowell. 



As />'. latcrale, but lateral stripe broken up on anterior fourth of length, after 

 which a trace only remains; labial ))late8 and throat unspotted; posterior 



labial plates more elongate Z. auri(/iihis Cope. 



V. Scales in 15 rows; superior labials 8 (form slender; color in stripes). 



Muzzle elongate, narrowed; frontal i)late more than half as wide as supercil- 

 iaries posteriorly; two lateral yellow stripes on a dark ventral and dorsal 

 ground; dorsal scales yellow-edged; no temporal spot. 



Z. scbottii Baird and (iieard. 



Muzzle elongate, flattened; frontal half as wide as superciliary behind; reddish 

 brown above and below, with two yellow stripes, as in Z. scltottii, that on the 

 third and fourth rows black-edged and split by a black line; colors above 

 alternately transversely darker and paler Z. oniatiis Haird and Girard. 



Muzzle depressed, short; frontal plate half as wide as superciliaries posteriorlv; 

 brown above to fourth row of scales; below and sides yellow ; later with four 

 or live lines (m middle of rows of scales Z. tacniatus Hallowell. 



