166 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



Rica at Cartago," Needless to say the dorsal scale formula of these 

 specimens should be carefully examined to make sure that they are 

 are not eques specimens with obscure stripes. As already stated, 

 it seems advisable to refer to eques the specimens from Zacaultipan, 

 Hidalgo, determined as sumichrasti by Cope. 



Affinities. — As already mentioned under the discussion of eques, I 

 believe that these two forms are directly related. They are remark- 

 ably similar except for the smaller dorsal scale formula and usual 

 obscurity of the dorsal stripe in su7nichrasti, and since I believe it 

 demonstrated that there is a tendency toward a reduction in the 

 number of dorsal scale rows and an obscuring of the stripes in eques 

 in southern Mexico, there can be no objection to considering the 

 individuals from Orizaba, Mexico, as representing the continuation 

 of this process. The form apparently lies entirely without the 

 province of eques, and intergrades with the latter through such 

 specimens as the ones from Hidalgo, valley of Mexico, etc., referred 

 by Cope to sumichrasti and pulchrilatus. Just where the intergra- 

 dation occurs can not now be determined, but it should be noted that 

 the difference in the number of scale rows must be brought about 

 in quite a narrow area, since the formula 19-17 is quite constant in 

 eques, even in the States of Hidalgo and Mexico, where it comes 

 close to the range of sumichrasti. 



PARIETALIS.a 



Description. — This form is so well defined that it has seldom been 

 confused with any other, and has avoided the fate of so many other 

 forms, i. e., being broken up into a number of subspecies. The dorsal 

 scale formula is always 19-17; the supralabials usually 7, frequently 

 8, but very rarely 6; the infralabials usually 10, occasionally 9, more 

 rarely 11, and very rarely 8; the ventral scutes 150 to 178; subcau- 

 dals 65 to 92; tail length .202 to .32. 



The general coloration is as follows : Ground color above dark olive 

 to brownish olive or dull reddish brown, the color being confined to the 

 scales between, and the keels of the scales involved in, the lateral 

 spots. The latter are arranged in two rows on the skin between the 

 lateral and dorsal stripes; occasionally the spots in both rows distinct, 

 but those of the upper row usually fused for more or less of their width 

 to form a black band, the spots of the lower row appearing as down- 

 ward projections from this band. The black pigment of the spots 

 only encroaches upon the edges of the involved scales. The inter- 

 spaces on the skin vary from orange to red, and this jiigment nearly 

 always encroaches on the edges of the involved scales. The ibst few 



« Thamnophis sirtalis parietalis (Say), Long's Exped. Rocky Mts., I, 1823, p. 186. 

 Includes Eutscnia sirtalis irilincata Cope (part), E. sirtalis tctratxnia Cope (part) (sco 

 also p. 176), and E- sirtalis dorsalis Cope (not E. dorsalis Baird and Gikard; see p. 158). 



