Selachoiday or Selachoidei: How To spell?

The word Selachoiday is misspelled against Selachoidei, a noun meaning "Same as Selachii."

Word ends with consecutive vowels 'EI' preceded by alphabets 'selachoid' is misspelled as 'AY'
Wrong Spelling:  selachoid-ay 
Correct Spelling:  selachoid-ei 
Find more incorrect spellings of Selachoidei to spell right way.