muskmelon vs rockmelon

muskmelon

noun
  • A type of melon, Cucumis melo subsp. melo, with sweet orange flesh and a rough skin resembling netting. 

rockmelon

noun
  • A type of melon, Cucumis melo var. reticulatus, with sweet orange flesh and a rough skin resembling netting. 

How often have the words muskmelon and rockmelon occurred in a corpus of books? (source: Google Ngram Viewer )