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Neidium iridis has a single broad, marginal longitudinal line.

Neidium amphigomphus has areolae that are transapically expanded near the valve margin.

Neidium fossum is smaller and has 2-3 longitudinal canals, with the innermost canal being notably wider.

LM scalebar = 10 µm
Neidium dilatatum 1 L1430 Neidium dilatatum 2 L1428 Neidium dilatatum 3 L1428 Neidium dilatatum 4 L1428 Neidium dilatatum 5 L1428 Neidium dilatatum 6 L1430 Neidium dilatatum 7 L1430
Length Range
154-231 µm
Width Range
40-49 µm
Striae in 10 µm
15-16

Neidium iridis

(Ehrenb.) Cleve 1894

Neidium iridis LM4 Neidium iridis LM5 Neidium iridis LM2 Neidium iridis LM3 Neidium iridis LM6 Neidium iridis LM1
Length Range
145-261 µm
Width Range
32-37 µm
Striae in 10 µm
12-13

Neidium amphigomphus

(Ehrenb.) Pfitzer emend. K.Lefebvre and P.B.Ham. 2015

Neidium amphigomphus LM6 Neidium amphigomphus LM5 Neidium amphigomphus LM4 Neidium amphigomphus LM3 Neidium amphigomphus LM2 Neidium amphigomphus LM1
Length Range
49.9-138.6 µm
Width Range
22-31.7 µm
Striae in 10 µm
15-16

Neidium fossum

Lefebvre and P.Ham. 2015

Neidium fossum LM6 Neidium fossum LM5 Neidium fossum LM4 Neidium fossum LM3 Neidium fossum LM2 Neidium fossum LM1
Length Range
66.7-129.7 µm
Width Range
20.1-24.9 µm
Striae in 10 µm
17-18