Compare

Cyclostephanos invistitatus and C. costalimbus both have a flat valve face. Cyclostephanos dubius has a lower fascicle density and alveolate striae. For comparison of C. tholiformis and C. delicatus, see text.

LM scalebar = 10 µm
Cytholiformis1 Cytholiformis2 Missrcytholiformis Cytholiformis 5 Cytholiformis 6 Cytholiformis 7
Diameter
9.1-15.3 µm
Striae in 10 µm
10-14 fascicles based on circumferential density

Cyclostephanos dubius

(Fricke) Round in E.C.Ther. et al. 1987

Cyclostephanos dubius LM5 Cyclostephanos dubius LM3 Cyclostephanos dubius LM4 Cyclostephanos dubius LM2 Cyclostephanos dubius LM1
Diameter
8.6-18.5 µm

Cyclostephanos invisitatus

(M.H.Hohn and Hellermann) E.C.Ther., Stoermer and Håk. 1998

Cyinvisitatus 1 Cyinvistatus 2 Cyinvisitatus 3 Cyinvisitatus 4A Cyinvisitatus 5 Cyinvisitatus 6
Diameter
7.8-15.1 µm
Striae in 10 µm
15-16 based on chord count, 12-15 based on circumferential density

Also compare to

Cyclostephanos costatilimbus

(H.Kobayasi & H.Kobayashi) Stoermer, Håk. and E.C.Ther.

Cyclostephanos delicatus

(Genkal) Håk. and H.J.Kling