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Variation and Distribution of the Middle American Snake Genus, Loxocemus Cope (Boidae?)

1967; Southwestern Association of Naturalists; Volume: 12; Issue: 4 Linguagem: Inglês

10.2307/3669610

1943-6262

Craig E. Nelson, John R. Meyer,

Lepidoptera: Biology and Taxonomy

Taxonomy and distribution of Loxocemus are reviewed. All speci- mens are assigned to L. bicolor. This species is known on the Pacific versant from Nayarit, Mexico, to Costa Rica and on the Atlantic versant from Chiapas, Mexico, and Honduras. Sexual dimorphism exists in spurs. No other geographically con- sistent secondary sexual dimorphism is known. Georgraphic variation exists in several characters of scutellation and relative proportion. Previous authors have proposed dividing Loxocemus into two species, subspecies, or phases, primarily based on supposed dichromatism; these divisions do not correspond with the geographic variation demonstrated in scutellation. Variation in coloration is not dichromatic but gradational. Prior fixing of the type locality of one of the synonyms, Plastoseryx bronni, is untenable. An examination of recently accumulated material of Loxocemus from Central America suggested that a re-evaluation of variation with- in the genus was advisable. This genus is usually placed in the Boidae but Romer (1956) placed it in the Aniliidae (sensu latu) and regarded it as structurally transitional to the Boidae. It differs from other New World boas in some characters that it shares with the Old World pythons (Romer, op. cit.). Although Bocourt (1882) and some other early workers considered all Loxocemus to be conspecific (summarized by Taylor, 1940), the recent trend, beginning with Taylor (op. cit.), has been to regard this genus as divisible into two forms which have been variously treated as species, subspecies (see synonomy) or di- morphic phases of one species (Zweifel, 1959; Duellman, 1961). The basis of this separation has been coloration, Iwith or without other pre- sumed differences. In both phases the dorsal surfaces of the head, body, and tail are usually uniform lavender-brown to grey-brown. Some specimens show irregular white spotting dorsally. In the dark or sumi- chrasti phase the venter is the same color as the dorsum, but is usually paler (Fig. 2). In the light or bicolor phase the supralabials and the ventral surface of the head, body and tail are immaculate white or