Next to Isotelus, Flexicalymene is the most common trilobite in the upper Ordovician. The same is not true in the Coburg formation as I have found only a few parts over the trips I've made. Below is a small, partially enrolled specimen that, unfortunately, is missing part of the cephalon. Based on William Hessin's book, "South Central Ontario Fossils", I think it may be Flexicalymene croneisi.
And this is an isolated pygidium.
The Coburg formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 172 to help identify them.