Complex sentence: In the Dumbarton Oaks mosaic the bust of Tethys, surrounded by fishes, is rising bare-shouldered from the waters; against her shoulder rests a golden ship's rudder.
Split into simpler sentences: In the Dumbarton Oaks mosaic, the bust of Tethys--surrounded by fishes--is rising, bare-shouldered from the waters. Against her shoulder rests a golden ship's rudder.