Xandarovula, Genus – synonym of Simnia, Genus
Xenocratena, Genus – synonym of Cuthona, Genus
Xiphiozona, Genus – synonym of Leptochiton, Genus
Xylotoma, Genus – synonym of Xylophaga, Genus
Xylotomea, Genus – synonym of Xylophaga, Genus
Xylotria, Genus – synonym of Pholas, Genus
Xylotrya, Genus – synonym of Bankia, Genus