Complex sentence: The Board of Regents acquired a portrait of Smithson dressed in Oxford University student attire, painted by James Roberts, that is now on display in the crypt at the Smithsonian Castle.
Split into simpler sentences: The Board of Regents acquired a portrait of Smithson, which shows Smithson dressed in Oxford University student attire. The painting, by James Roberts, is now on display in the crypt at the Smithsonian Castle.