This is from the biological taxonomy (Glaucopysche Xerces), so it is Latin or, more properly in this case, Latinized Greek. But it is pronounced like English. Biologists do not go around speaking in restored classical pronunciations. When is the last time you heard "sapiens" in "homo sapiens" pronounced with a broad "a" as in "father"? Or "tyrannosaurus" pronounced outside of Texas with like the "au" like the "aw" in "saw"? Or "biceps" pronounced "beekeps"? It just doesn't happen.
So, "kserses", with two short e's, accent on first syllable. Unfortunately, this will differ depending on the native language of the speaker. Even English pronunciation of Latin varies depending on which side of the pond you're on. For details, see: http://www.saltspring.com/capewest/pron.htm -Rob
