New state records of species of the flat-backed millipede family Paradoxosomatidae (Diplopoda: Polydesmida) are made for Mexico: Akamptogonus novarae (Humbert and Saussure, 1869) is recorded for the state of Nuevo Leon; Asiomorpha coarctata (Saussure, 1860) is recorded for the states of Estado de Mexico, Nuevo Leon, Tamaulipas and Oaxaca; Chondromorpha xanthotricha (Attems, 1898) is recorded for the states of Chiapas, Hidalgo, Nuevo Leon, Tamaulipas and Yucatan; and Oxidus gracilis (C.L. Koch, 1847) is recorded for the states of Coahuila and Tamaulipas. We also present two new cases of predation on Oxidus gracilis from a railroad worm (Coleoptera: Phengodidae) larva and a vinegaroon (Thelyphonida: Thelyphonidae).