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I am attaching images of Ordovician trilobites in my collection. I found the free, online Geological Survey Professional Paper 583-E to be very useful for identifying the Flexicalymene and Isotellus trilobites. Comments/suggestions/corrections are welcome. The 1st image is of Ordovician Flexicalymene meeki trilobites that I found in a creek bed in the Arnheim (sunset?) formation in Mt. Orab, Ohio. I identified these trilobites as F. meeki based on their relatively wide and sharp cephalons (heads). This is in contrast to the relatively narrow cephalons of F. retrorsa. The 2nd image is of a specimen collected on the same trip in the same same creek bed. The large fossil I have identified as the pygidium (tail) of the Isotellus maximus trilobite because it is not nearly as narrow and triangular as the pygidium of a I. gigantas trilobite. In the upper left is a prone flexicalymene trilobite that I have identified as an F. retrorsa due to the relatively narrow cephalon (compared to the body). If these identifications are correct then it is clear that all three species were contemporaneous. The third image is of a prone Flexicalymene retrorsa (my identification) trilobite from the Arnheim formation in Mt. Orab, Ohio. Note the relatively narrow cephalon (head). Image 4 is of a Isotellus maximus trilobite from the Ordovician Arnheim formation in Mt. Orab, Ohio. I identified this specimen based on the presence of genal spines on the cephalon as well as the relatively broad pygidium. Image 5 is of a larger, beat up Isotellus maximus trilobite from the Ordovician Arnheim formation in Mt. Orab, Ohio. I identified this specimen based on the presence of stubs of genal spines. Image 6 is of an Ordovician Cryptolithus instabilis trilobite from Buith Wells, Wales. I had previously found a small arc like fossil with perforations in Cincinnati and I had no idea about the source. I only recognized it after I saw the cephalon of the cryptolithus trilobite. This particular specimen has very little contrast with the bedrock so I altered the exposure and contrast in an effort to improve clarity. Image 7 is of a small, Ordovcian Amypxina bellatula trilobite from the Bellatula formation in Edgewood, MO. Image 8 is of a 505-438 MYA Diacalymene trilobite from the Ktaoua formation in Morocco.

A nice Dictyonema flabelliforme dendroid graptolite from Oslo Fields in Norway. It's Tremadoc, Lower Ordovician in age and is thus maybe around 480 mya. Another angle :