This is off Adorama's website ...
Mounts directly onto Canon EF Macro lenses: EF 50mm f/2.5 Compact Macro, EF 100mm f/2.8 Macro, EF 100mm f/2.8 USM Macro, and MP-E 65mm f/2.8 1 5x Macrophoto.
Attaches with accessory ring Macro Lite Adapter 72C to EF 180mm f/3.5L Macro.

Canon's website...
Attaches to all Canon EF macro lenses (EF 180mm f/3.5L requires Macro Lite Adapter 72C).

So, I don't think you needthe adapter except for use with the 180mm but with what Mark found...now I'm confused! [*-)]

I've been debating whether to purchase this or a new lens!

Denise