Triarthrus eatoni Trilobite from the Whitby formation

Certain layers within the Collingswood member of the Whitby formation are rife with the shed exuviae of the Trilobite Triarthrus eatoni. Like the similar (but older) rocks of the Utica shale in New York, most of the fossils are either partially or completely disarticulated. Most commonly found are articulated portions of the thorax/pygidium and disarticulated pieces of the cephalon.

Specimen #1 - A large slab with multiple examples

Note the disarticulated glabella from a Pseudogygites sp. Trilobite and Lingula cobourensis brachiopods.

Specimen #2 - Partial cephalon which is mostly just the glabella.

Specimen #3

Specimen #4

The Whitby 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. 205 to help identify these fossils.