You're welcome. I'm just glad to help. Sure, there are many dwarf boas out there that would be comfortable in the size you are talking about. I'm a boa guy, so it makes sense that I would suggest a boa. There are also many other species that would be comfortable in a 40 gallon. Check out this site for some info on dwarf boas: http://cuttingedgeherp.com/boaconstrictorimperator/. Let me know if you have any questions.