The Tres Marias Island boa. This subspecies is under taxonomical debate and is not accepted in full be either the scientific or herpetological community. There are no available records to show that this subspecies is in captivity either in the United States or abroad. The islands are make up a small group roughly 100 km off the Pacific coast of Mexico. Defined from 9 museum specimens. Scale count variance and not appearance is the main support behind this subspecies.
With an absence of specimens in culture it is hard to be certain, but most feel that Sigma is an island form of Mexican B.c.imperator.
Revisions to taxonomy and the elevation of imperator as a full species, the sigma classification was revisited as the name for Western Mexican boas.
Taxonomic data: Smith 1943; scale count 77 dorsal rows; 253-260 ventrals; 55-66 subcaudal; average 35 saddles.
