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U.S. Geological Survey Open-File Report 2012-1163

Stuart R. Stidolph Diatom Atlas


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This collection of light microscopy (LM) images of marine diatoms, made in the 1980s and 1990s, epitomizes the craftsmanship of the analog era of photomicrography. In the form presented here, it has become a peer-reviewed work, to which reference can be made in publications. The following notes supply the general information required for interpretation of the images.

Photomicrographic technique

All images were made with the following objectives: 20x/NA/0.70 and dry 40x/NA 0.95 planapochromatic, 90x/NA 1.4 apochromatic or a 60x/N.A. 1.4 planapochromatic oil immersion, combined with a 3.3x or 6.7x NFK photo eyepiece and enlarged to the magnification specified for the image in question. The film used was Kodak 2415 document film, developed in a slightly modified version of Kodak D19.

All images are unstacked - instead, images at different focus settings are presented in some cases. The photomicrographs were taken with conventional central brightfield illumination, phase-contrast or interference contrast were not used.


The legends mention magnifications for the various images. From these data, the optical combination used can be derived as follows:

90 x 6.7 = x2000               40 x 3.3 = x750

60 x 6.7 = x2000               20 x 6.7 = x500

40 x 6.7 = x1000               20 x 3.3 = x250

We have added scale bars to the plates representing 30 microns at 1000x and the correspondingly scaled value for the other magnifications.


Wherever possible Stidolph’s identifications were based on the illustrations supplied by the original author. If original data were unavailable, the reference source in closest agreement with the specimens was used.

In some cases, the identification was given by the maker of the slide, deposited in the collection mentioned. When Stidolph doubted this, a note was added. Where possible, we have verified this and commented accordingly. The references given by Stidolph are in a separate table, see further.

The identifications given have been updated, where Lyrella species were orignally assigned to the genus Navicula, for instance. We have added the current names and noted inconsistencies or questions in nomenclature. The authorship of the species in question was not given in the original text of the atlas and has also been added.


The materials are specified in the legends for the plates. Some specimens and slides represented are in the possession of S.R. Stidolph, although they will eventually be deposited in the Stidolph collection herbarium of the National Institute of Water and Atmospheric Research (NIWA), Christchurch, New Zealand. Specimens made from slides by other scientists are deposited in the collections specified.

The materials typically represent marine (sub)tropical habitats, the diatoms illustrated are typically inhabitants of the benthic or epipelic habitat.

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