drawing of <a href="//commons.wikimedia.org/w/index.php?title=Glochidium&amp;action=edit&amp;redlink=1" class="new" title="Glochidium (page does not exist)">glochidium</a> of <i><a href="//commons.wikimedia.org/wiki/Anodonta_cygnea" title="Anodonta cygnea">Anodonta cygnea</a></i>
<a href="//commons.wikimedia.org/w/index.php?title=Edward_Step&amp;action=edit&amp;redlink=1" class="new" title="Edward Step (page does not exist)">Edward Step</a> (1855-1931)
1901
Step. E.: <i>Shell life: an introduction to the British Mollusca</i>. - London, New York: F. Warne &amp; co. (1901), page 29, <a rel="nofollow" class="external free" href="https://archive.org/details/shelllifeintrodu00stepiala">https://archive.org/details/shelllifeintrodu00stepiala</a> exported from the pdf file in 600 dpi