De Ysalba

Does anyone know if the surname de Ysalba or de Esalba is a variation of de Alba?
I've got marriage entries for Maria de Ysalba with Joseph Feliz de Arrambide 02/20/1724 and 03/19/1720 in Mexico, DF.  Yet I can't find any de Ysalba's anywhere.  Both entries from two different churches in DF couldn't be wrong?   Your help would be greatly appreciated.    Alice Blake