Melon variety (6)
'melon variety' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for casaba that I've seen before include "fruit" , "Winter muskmelon" .)
(Other definitions for cantaloupe that I've seen before include "Musk-melon" , "fruit" , "musk melon" , "Type of melon" , "Small melon variety" .)