The title compounds were prepared by reaction of the elemental components at high temperatures. The compounds Yb2Ru3Ga10 and Lu2Ru3Ga10 crystallize with a new structure type, which has been determined from the single-crystal X-ray data of Yb2Ru3Ga10: P4/mbm, Z = 2, a = 881.9(1) pm, c = 632.5(1) pm. In this structure the gallium atoms form two-dimensionally infinite double layers that extend perpendicular to the tetragonal axis. They contain two-thirds of the ruthenium atoms. The other ruthenium and the ytterbium atoms are situated between the gallium double layers. The structure is closely related to that of Mn2Hg5. The latter compound may be written with the formula Mn(2)Mn(2)square Hg-10? thus indicating that its structure may be regarded as a defect-variant of the presently reported structure of Yb2Ru3Ga10. The four gallides of the series LnRu(2)Gas (Ln = La-Nd) crystallize with the orthorhombic CaCO2Al8-type structure (Pbam, Z = 4). This structure has been refined from single-crystal X-ray data of the cerium and neodymium compounds. Slight deviations from the ideal composition for one of the two ruthenium sites resulted in the formulas CeRu1.913(4)Ga8 and NdRu1.858(4)Ga8. Magnetic susceptibility measurements with a SQUID magnetometer indicate diamagnetism for LaRu2Ga8, which is partially compensated by the expected Pauli paramagnetism. The cerium atoms in CeRu2Ga8 show mixed or intermediate valent behavior, and PrRu2Ga8 follows the Curie-Weiss law with no magnetic order down to 4 K.