1	Even dorsal scale rows	2
–	Odd dorsal scale rows	6
2	Higher than 14 scale rows; apical pits presents; round pupil; black coloration and yellowish venter occasionally reaching dorso-lateral region	Spilotes pullatus pullatus
–	Fewer than 12 scale rows; keeled paravertebral scale rows; light vertebral stripe present	3
3	Brown head; grayish-black coloration bordering the light stripe up to 1/3 of body; brown on the remaining body; 12/12/8 scale rows, rarely 12/12/10	Chironius flavolineatus
–	Coloration not as above	4
4	12/12/10 scale rows; olive dorsum; light stripe bordered by black line; yellowish venter from labials; divided subcaudals with dark stripe between them	Chironius bicarinatus
–	12/12/8 or 14/12/8 scale rows	5
5	Olive dorsum at 1/3 of the body and brownish on the remaining portion; paravertebrals in lighter coloration; yellowish venter up to labials; dark stripe dividing dorsals and subcaudals; 132–144 ventrals	Chironius exoletus
–	Dark olive dorsum, lighter towards the venter; white chin; yellow venter; dorsal scales on tail with yellow center; 12/12/8 or 14/12/8 scale rows	Chironius carinatus
6	17 or less scale rows at midbody	7
–	19 or more scale rows at midbody	20
7	15 scale rows on midbody	8
–	17 scale rows on midbody	14
8	15/15/11 scale rows; keeled dorsal scales; metallic green with brown vertebral stripe; dark stripe above supralabials up to the end of head; big eye with round pupil	Leptophis ahaetulla liocercus
–	15/15/15 scale rows	9
9	Two black ring pattern separated by red rings; black rings separated by white or yellow rings; big and dark eyes; opisthoglyph dentition; 179–195 ventrals; 35–46 subcaudals	Erythrolamprus aesculapii venustissimus
–	Brown or green coloration, never red	10
10	Brownish head and dorsum; eliptical pupil; dark brown bands on dorsum; 163–182 ventrals; 59–77 subcaudals; single anal plate	Sibynomorphus neuwiedi
–	Ocelli or uniform pattern; divided anal plate	11
11	Brown head; Ocelli behind the head up to midbody; dorsum greyish to reddish-brown; yellowish venter; 160–173 ventrals; 70–77 subcaudals	Taeniophallus occipitalis
–	Not as above	12
12	Body uniform brown; pigmented head and nucal stripe; vertebral stripe; small eye; 138–156 ventrals; 50–63 subcaudals	Tantilla melanocephala
–	Uniform, ocelli or dark bands pattern	13
13	Dark brown or dark green coloration; juveniles present brown or redish bands separated by white or cream stripes; 157–180 ventrals; 86–110 subcaudals	Drymoluber dichrous
–	Brown head; dorsum light brown with dark ocelli; lateral blotches of the same color; venter lightly pigmented; ≥ 165 ventrals; ≥ 87 subcaudals	Mastigodryas bifossatus
14.	Without scale row reduction; vertebral scales modified; slender body; head strongly distinct; big eyes and elliptical pupil; brownish coloration with dark diamond shape blotches	Imantodes cenchoa cenchoa
–	With scale row reduction	15
15	17/17/13 scale rows	16
–	17/17/15 scale rows	17
16	Elongated head and slender body; big eyes with round pupil; brown coloration; chin and ventral gular portion yellowish or white; Dark oral mucosa	Oxybelis aeneus
–	Smooth scales; single anal plate; 2+2/2+3 temporals; postocular brown stripe; yellow gold coloration with black and yellow spots up to midbody	Thamnodynastes pallidus
17	Single anal plate; juveniles present yellowish coloration with darker transversal bands; adults present approximately dark anterior up to 2/3 of the body and yellow to the remaining portion; yellow venter	Drymarchon corais corais
–	Divided anal plate	18
18	Green-brownish coloration; single apical pit present; dorsolateral stripes from midbody to the end of tail; supralabials, chin and venter yellowish; Venter with alternating dark bands	Erythrolamprus reginae semilineatus
–	Without apical pits	19
19	Head light-brown; supralabials cream with black border; olive dorsum; black nucal stripe followed by a cream stripe; venter yellow-cream with black blotches	Erythrolamprus miliaris merremi
–	Dorsum black with transversal cream stripes; supralabials lighter than dorsum; white chin; reddish venter with 25–35 black bands	Erythrolamprus taeniogaster
20	Without apical pits	21
–	With apical pits	26
21	Single internasal scale	22
–	Pair of internasal scales	23
22	Dorsum light-brown or cream with dark blotches; scales strongly keeled; cream venter with black bands; 112–124 ventrals; 79–99 subcaudals	Helicops angulatus
–	Olive coloration with dark ocelli; scales weakly keeled; red venter with black bands; white chin; 121–133 ventrals; 57–79 subcaudals	Helicops leopardinus
23	Brown coloration lighter on the head; white or cream supralabials, chin and venter; modified rostral scale; smooth scales	Phimophis guerini
–	Regular rostral scale	24
24	Green coloration; juveniles present dark green with black spots along the body; supralabials, chin and anterior portion of body yellowish; 19/19/17 scale rows; >176 ventrals	Erythrolamprus viridis viridis
–	Other color pattern	25
25	Top of the head brown with a cream or white V or Y shape mark; Dorsum present brownish bands divided by grayish stripes; dorsolateral cream stripes; orange-reddish venter with black bands; 19/19/17 scale rows	Erythrolamprus almadensis
–	19/19/15 scale rows; Brownish coloration, occasionally with diagonal black ribs; cream venter weakly pigmented	Erythrolamprus poecilogyrus schotti
26	Single apical pit	27
–	Two apical pits	30
27	Body uniform green, venter in lighter coloration; long tail; divided anal plate; 164–208 ventrals; 92–132 subcaudals	Philodryas olfersii herbeus
–	Brown pattern, never green	28
28	Brown head; coloration varies from uniform brown to grayish; White venter; divided anal plate; 166–189 ventrals; 76–113 subcaudals	Philodryas patagoniensis
–	19/19/17 scale rows arranged in oblique rows	29
29	Head with small blotches and stripes from internasals to postocular portion; brown coloration with bow shape blotches connected bilaterally or usually alternated	Xenodon merremii
–	Single blotch on head bifurcated on the neck; Brown dorsum with dark bow shape blotches along the body; pigmented venter	Xenodon rhabdocephalus rhabdocephalus
30	Modified vertebral row; orange head; juveniles present white stripe on parietals; black nucal stripe and red-wine coloration with black bands; white venter; >230 ventrals; >105 subcaudals	Siphlophis compressus
–	Vertebral scales not modified	31
31	Keeled scales in 19 or 21 rows; brown head; Internasals, prefrontals and labials pigmented; black postocular stripe present; dark-brown dorsum, yellowish towards the venter with black diagonal stripes	Spilotes sulphureus sulphureus
–	Smooth scales	32
32	19 or 21 scale rows; brown head, darker on parietals; juveniles present white stripe on parietals; brown coloration with dark blotches	Leptodeira annulata annulata
–	Pattern black, brown or with red, black and white rings	33
33	21 scale rows; brown head with white stripes above the eyes up to parietals; white supralabials weakly pigmented; brown-grayish coloration with dorsolateral dark stripes and white paraventral stripe; white venter with dark stripe on edge of ventrals	Philodryas nattereri
–	19 scale rows, single anal plate	34
34	Uniform coloration with or without irregular spots	35
–	Pattern of black, red and white rings, white venter	36
35	Black or dark-brown coloration; juveniles present a white stripe on head, dark nucal stripe and red-wine coloration; 207–235 ventrals; 53–81 paired subcaudals	Clelia plumbea
–	Black coloration with or without white blotches; juveniles present a white stripe on head, dark nucal stripe and red-wine coloration; 188–202 ventrals; 81–97 single subcaudals	Pseudoboa nigra
36	Black head up to parietals; supralabials grayish; red nucal stripe; triad of black and white rings separated by red rings; white chin	Oxyrhopus trigeminus
–	Black head with red nucal stripe; juveniles present black and white coloration; adults present black and red coloration	Oxyrhopus petolarius digitalis