Perisodactyla or Perissodactyla: How To spell?
The word Perisodactyla is misspelled against Perissodactyla, a noun meaning "A division of ungulate mammals, including those that have an odd number of toes, as the horse, tapir, and rhinoceros; -- opposed to Artiodactyla."
Perissodactyla has double "ss" is mispronounced as "s"Remember double 'SS' in between the strings peri & odactyla which should not be misspelled with single 'S'
Wrong Spelling:  peri-s-odactyla  Correct Spelling:  peri-ss-odactyla 
Find more incorrect spellings of Perissodactyla to spell right way.