28. COLUBER 



markings on the rest of the underside are very dense, leav- 

 ing only a pale line on the angle of the belly, or are con- 

 densed into two fairly distinct parallel longitudinal bands 

 with a pale zone down the middle of the body. 



Length to anus 1090 



Length of tail 360 



Distribution. — This snake has been found only on Clar- 

 ion Island of the Revilla Gigedo group, ofF the western 

 coast of Mexico. 



147. Coluber semilineatus (Cope) 

 SoNORAN Racer 

 Plate 67 



Bascanium laniatum laterale Yarrow, Surv. W. looth Merid., Vol. V, 



1875. P- 543 (part). 

 Bascanion semilineatum Cope, Proc. U. S. Nat. Mus., Vol. 14, 1892, 



p. 626 (type locality, Colorado River and Camp Grant, Arizona) ; 



Van Denburgh, Proc. Cal. Acad. ScL, Ser. 2, Vol. 6, 1896, p. 347; 



Van Denburgh, Proc. Acad. Nat. Sci. Phila., 1897, p. 463; Stej- 



NEGER, Proc. U. S. Nat. Mus., Vol. XXV, 190a, p. 155; Stone, 



Proc. Acad. Nat. Sci. Phila., 191 1, p. 231; Van Denburgh & 



Slevin, Proc. Cal. Acad. Sci., Ser. 4, Vol. 3, 1913, p. 417. 

 Zamenis semilineatus Gunther, Biol. Centrali-Amer., Rept., 1894, p. 



121, pi. XLVI, fig. A; Cope, Report U. S. Nat. Mus., for 1S98, 



1900, p. 805, fig. 417. 

 Coluber semilineatus Stejneger & Barbour, Check List N. Amer. Amph. 



Rept., 1917, p. 80. 



Description. — Head long, with flattened top, and nar- 

 row, rounded snout. Rostral plate large, high, hollowed 

 below, and bounded behind by internasal, anterior nasal, and 

 first labial plates. Plates on top of head are a pair of inter- 

 nasals, a pair of much larger prefrontals, supraocular and 

 part of upper preocular of each side, long frontal, and pair 

 of large parietals. Anterior and posterior nasals distinct. 



