1) Callipygous 2) Shapely 
Having well-shaped beautiful buttocks. This fascinating obscure term (thanks S Marcus, PhD) - indeed the OED categorises the adjective as 'rare' - deserves wider exposure. Callipygian is pronounced 'Kallipijian' with the emphasis on the 'pij' syllable. A more recent variation is Callypygous ('kallipijus'). The word came into English in the late 170...
callipygian 1. A reference to or having finely developed buttocks or rear end. 2. Having beautifully proportioned buttocks.
callipygous adjective pertaining to or having finely developed buttocks; `the quest for the callipygian ideal`