The word protostrophis is spelled with a silent "o" in its second syllable, despite it being pronounced as "pro-tuh-stroh-fis". The IPA phonetic transcription of this word is /proʊtəstroʊfɪs/. The "o" in the middle of the word is there to break up the consonant cluster between "t" and "s", creating a more fluid pronunciation. This kind of spelling can often trip up learners of English, but understanding the phonetic transcription can help to clarify and make sense of it.
In bot., a spiral vessel separating from the main bundle that enters the leaf, and forming part of the primary veins.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.