In the German language the word bull snake is used for all of the members of the genus Pituophis
In America the following groups of the Pituophis are seperated:
Here I use the american words Pine-, Bull- + Gopher Snakes.
But not every author and every language use the same names for those snakes. So the only sure name for an animal is it's sientific name, in latin.The genus Pituophis had it's first discripion by Holbrook, 1842 with the Pituophis melanoleucus melanoleucus, the northern pine snake.
The name Pituophis most authors adapted of the latin words pituitarius= "hissing" und ophis = "snake".
The genus has at this time (aprox.) 19 subspecies in 5 species, wich were distributed in a great part of North America.
The systematic of the genus Pituophis is overworked several times and it's actual status is changing nearly every year. And because of the use of different modern methods not all sientists get the same solutions or agree the dates of the colleges.
And not every systematic change finds it's way into our terrariums...
Long years the species melanoleucus and catenifer were seperated from each other. In the begin of the 2nd half of the 20. Century the subspecies of the the genus catenifer were transfered to the genus melanoleucus. Today those both species are seperated again. Furthermore there are the species ruthveni, deppei und lineaticollis.
One of the latest and important great works about this genus is:(Rodriguez, 2000): Molecular Systematics of New World Gopher, Bull, and Pinesnakes (Pituophis: Colubridae), a Transcontinental Species Complex.
I thank for the publication of this important work in the internet! One of the renew details in there were, that the subspecies ruthveni became the genus Pituophis ruthveni. This opinion is followed by most of the sientistis. The bull snake now ist too in the EMBL-Datenbank transfered to the genus catenifer. Some authors gave it a species status, mut not many (international) sientists agree. (Grismer, 1997) removed the status of a subspecies of bimaris (from the Baja California) and put them all as an color variant to the vertebralis. Furthermore the island form insulanus he set on species status.
But, too, those both changes are still in an international discussion...
For the systematic of the genus Pituophis I use on my homepage the actual EMBL-Datenbank. This source should give the sure actual status of the species and subspecies.