Reply To: Ordovician, southwestern Wisconsin,

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#24062
Asa Kaplan
Participant

That pygidium is definitely not Flexicalymene! Note in this photo how triangular Flexicalymene‘s pygidium is, and how it terminates with a prominent bulb on the median lobe with hardly any posterior margin. The pygidium you show has many segments and a broad posterior margin — features typical of order Proetida, not Phacopida (of which Flexicalymene is a member). I was not able to locate an Ordovician trilobite to match your image, but I’ve included below an image of a pygidium that more closely matches the features I see in yours. (This pygidium belongs to Dikelocephalus, which is certainly not the trilobite in your hand.)

Image result for flexicalymene pygidium

https://upload.wikimedia.org/wikipedia/commons/d/df/Flexicalymene_meeki_pygidium_view.JPG

https://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Dikelocephalus_minnesotensis_pygidium_draw.png/440px-Dikelocephalus_minnesotensis_pygidium_draw.png