From @ian_gardiner on inaturalist: "At max magnification you can see denticles on the head in front of the eye - which indicates S. serrulatus. The head shape is also exactly right for serrulatus. But serrulatus has an obvious prominence around the middle of the posterior margin of the carapace. I don't see that here, all I see is a small prominence close to the dorsal margin.

From the neck up it looks like serrulatus, but from the neck down not so much. However, BOLD systems does have images of serrulatus with a posterior margin like your specimen:

http://v3.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxid=51840

So it seems that the prominence on the posterior margin is not an infallible guide to serrulatus. So I'll go with serrulatus."