Complex sentence: They arrived in S.A. on the ship "Ariadne" in August 1839; their party, which included more than those listed above, had set out for S.A. in April.
Split into simpler sentences: They arrived in S.A. on the ship "Ariadne" in August 1839. The "Ariadne" party, which included more than those listed above, had set out for S.A. in April.