Table 2 in Systematic revision of the snorkel snail genus Rhiostoma Benson, 1860 (Gastropoda, Caenogastropoda, Cyclophoridae) with descriptions of new species

Table 2. Comparative shell morphology among six genera that are superficially similar to Rhiostoma. The characters are mainly based on the type species. The tribe classification for each genus follows Bouchet et al. (2017). References: 1 Benson (1860); 2 Möllendorff (1885), Kobelt (1906) and Yen (1939); 3 Kobelt (1902), Thiele (1929), Wenz (1938) and Egorov (2009); 4Kobelt (1912), and Low and Tan (2017); 5 Gude (1921) and Kobelt (1911).
PterocycliniCyclotiniCyclophoriniPterocyclos Benson, 18323,5Spiraculum Pearson, 18333,5Rhiostoma Benson, 18601,3,5Cyclotus Swainson, 18403,5Opisthoporus Benson in Pfeiffer, 18513,4Ptychopoma Möllendorff, 18852,3Type speciesPterocyclos rupestris Benson, 1832Spiraculum hispidum Pearson, 1833Rhiostoma haughtoni Benson, 1860Cyclotus variegatus Pearson, 1833Cyclostoma taylorianus Pfeiffer, 18515Cyclophorus chinensis Möllendorff, 1874Shell shapediscoidaldiscoidaldiscoidaldiscoidal to turbinatediscoidaldiscoidalPeriostracumthick to thin corneousthick corneous and hairythin corneousthin corneousthick corneous and hairythick corneousDetached whorlabsent to shortabsent*absent to extremely long (curved and descending)absent to shortabsent to shortabsentBreathing device:sutural tubeabsentpresentabsentabsent**absentabsentupper junction of peristomeexpanded, thickened and free or attached to preceding whorlexpanded and attached to preceding whorlthickened, free or attached to preceding whorlexpanded and free or attached to preceding whorlexpanded and free or attached to preceding whorlthickened and attached to preceding whorlOuter peristomewidely expanded with wing or hoodexpanded with wing or hoodthickened with knob, notch or tubeexpandedexpanded with tube located close to lipinconspicuousInner peristomeshallow to deep incisionshallow to deep incisionshallow to deep incisionshallow incisionshallow incisioninconspicuousOperculumcalcareous (thin), concave to low cup-shaped with elevated lamella, lateral fringe straightcalcareous (thin), concave to low cup-shaped with elevated lamella, lateral fringe straightcalcareous (thick), tall to low cup-shaped with elevated lamella, lateral fringe straightcalcareous, concave without elevated lamella, lateral fringe with deep groovecalcareous, concave without elevated lamella, lateral fringe with deep groovecorneous, plate-shaped with low lamellaDistributionSouth Asia to southern China and IndochinaSouth Asia to Indochinaprincipally in IndochinaAsia to Australiaprincipally in IndochinaSouthern China to Japan
* Spiraculum mastersi Blanford, 1877 from India have a short, detached whorl (see Sutcharit et al. 2019: fig. 9a). ** Cyclotus birostris (Pfeiffer, 1855) from Borneo have sutural tube projecting anteriorly (see Sutcharit et al. 2019: fig. 2j, k).