Quaternary selenides Sn 2 Pb 5 Bi 4 Se 13 and Sn 8.65 Pb 0.35 Bi 4 Se 15 were synthesized from the elements in sealed silica tubes; their crystal structures were determined by single-crystal and powder X-ray diffraction. Both compounds crystallize in monoclinic space group C2/m (No.12), with lattice parameters of Sn 2 Pb 5 Bi 4 Se 13 : a=14.001(6)Å, b=4.234(2)Å, c=23.471(8)Å, V=1376.2(1)Å 3 , R 1 /wR 2 =0.0584/0.1477, and GOF=1.023; Sn 8.65 Pb 0.35 Bi 4 Se 15 : a=13.872(3)Å, b=4.2021(8) (4)Å, c=26.855(5)Å, V=1557.1(5)Å 3 , R 1 /wR 2 =0.0506/0.1227, and GOF=1.425. These compounds exhibit tropochemical cell-twinning of NaCl-type structures with lillianite homologous series L(4, 5) and L(4, 7) for Sn 2 Pb 5 Bi 4 Se 13 and Sn 8.65 Pb 0.35 Bi 4 Se 15 , respectively. Measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps; Sn 2 Pb 5 Bi 4 Se 13 is n-type, whereas Sn 8.65 Pb 0.35 Bi 4 Se 15 is a p-type semiconductor with Seebeck coefficients −80(5) and 178(7)μV/K at 300K, respectively.