Compare

Semiorbis eliasiae is less strongly arched and has a smaller size range. Semiorbis catillifera valves are weakly arcuate. Semiorbis hemicyclus has valves that are slightly less curved and less protracted, however, note that this taxon has not been documented in North America.

LM scalebar = 10 µm
Semiorbis rotundus LM7 Semiorbis rotundus LM6 Semiorbis rotundus LM4 Semiorbis rotundus LM3 Semiorbis rotundus LM2 Semiorbis rotundus LM5 Semiorbis rotundus LM1
Length Range
32.9-45.1 µm
Width Range
3.9-4.8 µm
Striae in 10 µm
12-13

Semiorbis eliasiae

Edlund, D.R.L.Burge, N.A.Andresen and VanderMeulen 2021

Semiorbis eliasiae LM1 Semiorbis eliasiae LM2 Semiorbis eliasiae LM3 Semiorbis eliasiae LM4 Semiorbis eliasiae LM5 Semiorbis eliasiae LM6
Length Range
16.5-40.5 µm
Width Range
3.5-5.7 µm
Striae in 10 µm
8-12

Semiorbis catillifera

(Morrow) G.Reid and D.M.Williams 2010

Semiorbis catillifera LM1 Semiorbis catillifera LM2 Semiorbis catillifera LM3 Semiorbis catillifera LM4 Semiorbis catillifera LM5 Semiorbis catillifera LM7 Semiorbis catillifera LM6
Length Range
17-40 µm
Width Range
4.8-5.3 µm
Striae in 10 µm
12-13

Also compare to

Semiorbis hemicyclus

(Ehrenberg) R.M.Patrick in Patrick and Reimer

BioData Reference
Reid and Williams 2010 Fig 9-13