Looks like it could be Austrocylindropuntia subulata, as seen at this link: http://www.f-lohmueller.de/cactus/Opuntia/imf_cod2.htm
I snapped this a few minutes ago. It is pretty dark in the greenhouse so my appolgies. This cactus is an animal--42 inchess in a year! Not sure how long I can support it. I would agree with the last post for ID. Bill