The venter is immaculate white or pale yellow and the dorsum of the body is immaculate pale gray to pale olive. Some specimens have small dark brown spots on the tips of the scales of the 4th or of the 7th row, but never on both. Only on the nape are spots present on both the 4th and the 7th rows; these spots are the posterior continuations of the dark stripes on the head and on many specimens do not reach the nape. Posterior to the place of scale reduction from 19 to 17 rows by the fusion of the 3rd and 4th rows of scales, the dark spots (when present) are on the 3rd or 6th row of scales.
The coloration of juveniles is the same as that of adults. Color in life is thought not too different from that of preserved specimens, for notes on the color of living individuals (Neill and Allen, 1961:44) agree with what I have observed on preserved snakes.
Remarks.—The specimen from "Petén" (USNM, no. 4941) is the only specimen that has a controversial history. As can be seen from the synonymy of the species, the relationship of this specimen with the rest of the genus has been interpreted in several ways. Smith (1941:122-123) stated that the above specimen was catalogued as being from El Salvador; however, the locality was presumed by him to be El Petén, Guatemala, due to the presence in the bottle of a piece of paper inscribed "Conophis vittatus, Petén, J. M. Dow." This specimen is the one mentioned by Cope (1861:300, 1876:76, and 1900:1094-95), and in the first paper is ascribed to Guatemala. In 1900 this specimen was named C. lineaticeps by Cope who thought the specimen differed significantly from C. concolor (Cope, 1867:318-319). This specimen has the coloration normal for C. l. concolor as far posteriorly as mid-body; beyond mid-body the dark lines, typical of C. l. lineatus or of C. l. dunni, are present. It is likely that this specimen is an intergrade between C. l. concolor and C. l. dunni, the other subspecies present in Guatemala.
The only specimen not from the Yucatán Peninsula is allegedly from Patuca, Honduras (USNM 20271). It was obtained in the 1870's. Possibly more collecting will verify the presence of C. l. concolor in northern Honduras. This individual may be merely a genetically aberrant specimen from an area where normal specimens are C. l. dunni. Neill and Allen (1961:44-45) suggested that the specimen from Patuca implies widely overlapping distributions for C. l. dunni and C. concolor. The occurrence of C. l. concolor in Honduras needs to be verified before this assumption is made. There can, therefore, at present be no objection to the view that intergradation between the subspecies C. l. dunni and C. l. concolor could occur through a relatively broad area of El Petén and British Honduras.
Neill and Allen (1961:44-45) further suggest that the present range of C. l. dunni extends "presumably still farther northward toward the Méxican state of Veracruz where C. l. lineatus exists." Actually the presence of the subspecies C. l. dunni and C. l. lineatus as presently disjunct populations implies merely that they were presumably a continuous population at some time in the past.
The characteristics of the genus in combination with the reduction of dark coloration posterior to the head distinguish this snake from all other snakes in México and Central America.
Distribution.—The Yucatán Peninsula: eastern Campeche, all of Yucatán, probably in Quintana Roo, and the northern third of British Honduras. A record for northeastern Honduras is questioned ([fig. 2]).
Specimens examined.—Total of 48, as follows: British Honduras: Belize District: 13.0 mi. W, 1.5 mi. S Belize, ERA-WTN BH-1562.
Guatemala: El Petén, no specific locality, USNM 4941.
Honduras: Colón: Patuca, USNM 20271.