Crosopterygii or Crossopterygii: How To spell?
The word Crosopterygii is misspelled against Crossopterygii, a noun meaning "An order of ganoid fishes including among living species the bichir (Polypterus). See Brachioganoidei."
Crossopterygii has double "ss" is mispronounced as "s"Remember double 'SS' in between the strings cro & opterygii which should not be misspelled with single 'S'
Wrong Spelling:  cro-s-opterygii  Correct Spelling:  cro-ss-opterygii 
Find more incorrect spellings of Crossopterygii to spell right way.