Crossopterygi or Crossopterygii: How To spell?
The word Crossopterygi is misspelled against Crossopterygii, a noun meaning "An order of ganoid fishes including among living species the bichir (Polypterus). See Brachioganoidei."
Crossopterygii has double 'ii' in the end mispronounced as 'i'Remember double 'II' appears in the end of this word which should not be misspelled with single 'I'
Wrong Spelling:  crossopteryg-i  Correct Spelling:  crossopteryg-ii 
Find more incorrect spellings of Crossopterygii to spell right way.