rhytidiadelfis: how many corrections?
heard as rhytidiadelfis
spelled rhytidiadelphus
Two. The f is written ph and the last vowel is u. Rhytidiadelphus.
What the ear did
The end of a long name is where attention runs out, and this rendering shows it: the difficult opening is intact, the last two syllables have collapsed into whatever the mouth produced.
R-H-Y-T-I-D-I-A-D-E-L-P-H-U-S
The full entry for rhytidiadelphus covers the name itself.