44 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



/'. Lateral spots fused into transverse l)lotclies for the entire length. . 



scalaris, p. 127. 

 (Southern Mexico and northern Central America.) 

 /-'. Lateral spots not fused into transverse blotches for the entire length. 

 g^. Both rows of lateral spots distinct on the skin; interspaces not gen- 

 erally red sirtalis, p. 17G. 



(North America east of 91st meridian and south of the 52nd par- 

 allel.) 

 g"^. Upper row of lateral spots usually fused on the skin; interspaces red. 

 hK Dorsal stripe usually covering one and two half-rows. Width of 



interspaces on skin equal to the length of one scale 



parietalis, p. 166. 

 (From the 91st meridian to the Pacific coast, exclusive of 

 western Oregon and Washington, and south of the 52nd par- 

 allel.) 

 h^ Dorsal stripe usually confined to one row. Width of interspaces on 

 skin generally less than the length of one scale, frequently ab- 

 sent concinnus, p. 173. 



(Western Oregon and Washington.) 



d"^ Frequently 2 preoculars ordinoides, p. 147. 



(California, Oregon, and Washington, west of the Sierra Nevada-Cascade 

 Range.) 

 c^ Dorsal stripe usually absent, 

 d' Dorsal scale rows 19-17. 



e^ Lateral spots fused into transverse liars, which usually extend entirely 



across the back phcnax, p. 130. 



(Veracruz, Mexico.) 



e^ Lateral spots not fused into transverse bars iiKlnnof/astcr, p. 124. 



(Southern Mexico.) 



d- Dorsal scale rows usually 17-19-17 or 17-15 sumichrasti, p. 164. 



(Southern Mexico.) 



THE RADIX GROUP (MEGALOPS, MARCIANUS, RADIX, AND BUTLERI). 



MEGALOPS.a 



Description. — The Mexican plateau, possibly on account of its topo- 

 graphic unity, is the home of one of the most homogeneous forms in 

 the genus, notwithstanding the fact that this form has been divided 

 into four species {megalops and macrostemma Kennicott, and jiavi- 

 lahris and insigniarum Cope). This form, if we succeed in establish- 

 ing its unity, should be known as megalops, and is undoubtedly 

 the largest of the garter-snakes. It is characterized in general 

 by having the lateral stripe on the third and fourth rows, mostly 

 21-19-17 scale rows, 8 or 9 supralabials, 152 to 174 ventrals, 60 to 

 87 subcaudals, and a proportionate tail-length of .20 to .278. 

 There is considerable variation in color, so that no single description 

 can be given that will apply for the form. For detailed description 

 see page 55. 



Habits and habitat relations. — As is usually the case among reptiles, 

 but little has been recorded concerning the habits of inegalops, which 



o Thamnophis megalops (Kennicott), Proc. Acad. Nat. Sci. Phila., 1860, p. 330. In- 

 cludes E. macrostemma Kennicott, E. insigniarum Cope, and E. flavilabris Cope. 



