Crotalus pusillus
Crotalus pusillus, or the Tancitaran Dusky Rattlesnake, is a venomous pit viper species found in west-central Mexico. No subspecies are currently recognized. Description 
Adult males may grow to more than  in length, while females are smaller. The largest recorded length for a specimen was . Behavior 
Campbell and Lamar (2004) found this species only to be active during the day. Within its range, night temperatures are low and seem to restrict its activity. Geographic range 
It is found in west-central Mexico in the Sierra de Coalcomán of southwestern Michoacán, the Transverse Volcanic Cordillera of west-central Michoacán, and in adjacent Jalisco. It is probably also found in northeastern Colima. Its type locality is reported as "Tancítaro, Michoacán, Mexico, altitude 5,000 ft" (5,000 ft = 1,524 m). It occurs at elevations between . Conservation status 
This species is classified as Endangered on the IUCN Red List of Threatened Species. The population trend was unknown when assessed in 2007. References

Further reading 
 Klauber, L.M. 1952. Taxonomic studies on rattlesnakes of Mainland Mexico. Bull. Zool. Soc. San Diego 26:1-143. External links 
 

pusillus
Reptiles described in 1952