10. TROPIDONOTTTS. 205 



6. Tropidonotus ordinatus. 



Coluber ordinatus, Limi. S. N. i. p. 379 (1766). 



Tropidonotus bipunctatus, Schleg. Phys. Serp. ii. p. 320 (1837) ; 



Bum. S,- Bihr. vii. p. .582 (1854). 



ordinatus, part., Gilnth. Cat. p. 73 (18o8). 



sirtalis, part., Jan, Arch. Zool. An. Phys. iii. 1865, p. 210 ; 



Garm. N. Am. Pept. p. 24 (1883). 

 Eutsenia sirtalis, Cope, Wheeler's Rep. U.S. Surv. W. lOWi Mer. 



V. p. 540 (1875), and Proc. U.S. Nat. Mus. xiv. 1892, p. 661. 



Eye moderate or rather large. Rostral broader than deep, 

 visible from above ; internasals as long as broad or broader, as long 

 as or shorter than the priefrontals ; frontal once and a half to once 

 and three fourths as long as broad, as long as its distance from the 

 end of the snout, shorter than the parietals ; lorcal about as long 

 as deep ; one prse- and three (rarely four) postoculars ; temporals 

 1+2 or 1 + 3; seven or eight upper labials, two entering the eye; 

 five (rarely four) lower labials in contact with the anterior chin- 

 shields, which are shorter than the posterior. Scales in 19 or 21 

 rows, strongly keeled : the keel on the outer scale, if present, 

 weaker than on the others. Ventrals 137-176 ; anal entire ; sub- 

 caudals 44-100. Coloration very variable ; a pair of light dots on 

 the suture between the parietal shields is nearly constant. 



Total length 950 miUim. ; tail 190. 



North and Central America. 



This species may be divided into numerous forms or varieties, of 

 which the following are the principal : — 



I. Lateral stripe, if distinct, running along the second and third 

 rows of scales. 



A. Scales in 19 rows (exceptionally 21). 



1. Seven upper labials, third and fourth entering the eye ; 



scales of outer row keeled. 



No vertebral stripe A. Forma typica. 



A light vertebral stripe B. sirtalis. 



2. Seven or eight upper labials ; scales of outer row smooth or 



feebly keeled ; a light vertebral stripe, occupying one 

 and two half scales C. infernalis. 



3. Eight (rarely seven) upper labials ; vertebral stripe, if 



present, one scale wide. 



A light vertebral stripe D. eques. 



No vertebral stripe ; no cross bands E. sinnichrasti. 



No stripe, but cross bands F. phenax. 



B. Scales in 21 rows ; eight upper labials, fourth and fifth 



entering the eye ; dorsal stripe, if present, narrow. 



A narrow yellow dorsal stripe ; belly greyish 



olive or black G. couchii. 



