Complex sentence: He worked closely with Thomas Barbour, the museum's director, with whom he had a warm relationship; after Barbour's death in 1946, Griscom reported to the new director, Alfred Romer.
Split into simpler sentences: He worked closely with Thomas Barbour, the museum's director, with whom he had a warm relationship. After Barbour's death in 1946, Griscom reported to the new director, Alfred Romer.