Subgenus Monoplex G. Perry, 1811

Type species: Cymatium (Monoplex) parthenopeum parthenopeum (von Salis, 1793) Cymatium (Monoplex) parthenopeum echo Kuroda & Habe in Kira, 1961 Cymatium (Monoplex) parthenopeum keenae (Beu, 1970)
Cymatium parthenopeum parthenopeum Cymatium parthenopeum echo Cymatium parthenopeum keenae
Type Species    
Living Specimen | Shaggy Periostracum    
Cymatium (Monoplex) amictum (Reeve, 1844) Cymatium (Monoplex) aquatile (Reeve, 1844) Cymatium (Monoplex) corrugatum (Lamarck, 1816)
Cymatium amictum Cymatium aquatile  Cymatium corrugatum
Cymatium (Monoplex) gemmatum (Reeve, 1844) Cymatium (Monoplex) intermedium (Pease, 1869) Cymatium (Monoplex) krebsii (Mřrch, 1877)
Cymatium gemmatum Cymatium intermedium Cymatium krebsii 
Cymatium (Monoplex) macrodon (Valenciennes, 1832) Cymatium (Monoplex) martinianum (d' Orbigny, 1847) Cymatium (Monoplex) mundum (Gould, 1849)
 Cymatium macrodon Cymatium martinianum Cymatium mundum
Cymatium (Monoplex) nicobaricum (Röding, 1798) Cymatium (Monoplex) pileare (Linnaeus, 1758) Cymatium (Monoplex) tranquebaricum (Lamarck, 1816)
Cymatium nicobaricum  Cymatium pileare Cymatium tranquebaricum
Cymatium (Monoplex) trigonum (Gmelin, 1791) Cymatium (Ranularia) turtoni (E. A. Smith, 1890) Cymatium (Monoplex) vestitum (Hinds, 1844)
 Cymatium trigonum Cymatium turtoni Cymatium vestitum