I managed to spend eight hours at my secret Onondaga spot yesterday. I am starting to lose shoreline as the water levels rise, which is not great in terms of short term collecting as it means only exposing material above the highest watermark which is brutally hard. However, it is good in the long term as it may soften up a few more rocks when they are submerged, making splitting more of a joy when the waters subside again, likely in autumn. But there was still enough material to play with yesterday.
Brachiopods are by far the most abundant fauna in this material. The big, round globular kind leave huge globular divots in the impression side of the bedding plane.
Rostroconch seem to be following me around this year. I still pocket the smaller brachs pictured at the bottom if they are matrix-free and possess both valves.
Here is a monster-conch. 4.5 cm wide, or nearly 2 inches. I was able to free most of it from the matrix. The upper portion comes off like a lid so that one could see the detailed structure inside.
Coronura fragments, and this is not even all of them. Some I even left in the field. It is immensely frustrating to go through so much volume of rock and never find much more than this intact.
Odontocephalus cephalic denticle brims.
This is where the revision part comes in. I've been casually assuming all this time that these were Anchiopsis anchiops. Well, hold on there. These are actually likely to be Odontocephalus pygidia.
More to the point, a morphological comparison of an Anchiopsis I found recently at another location, and on the right the Onondaga material. The main differences include width and terminal caudal spine. The former seems obvious here, but the latter was the source of my error. I had thought the pointy tip of the spine was just too delicate, resulting in getting broken, but each of my Onondaga specimens where the spine is present has this notch in place of a pointed tip. Also, note the relative robust width of the base of the spine in relation to the pygidium. Reexamining all of my assumed Anchiopsis bits leads me to the conclusion that this material does not possess this taxon, but that it is in fact Odontocephalus as the only other match among the synphoriinae that has this notched bottom at the end of a longer spine.
And now for the oddball. Just as I can cross off one species from the list at this location, I can add one more. It was getting late in the day, and my eyes were getting as tired as my hammering arm. I nearly tossed this aside as just another Pseudodechenella pygidium but instinct had me look much closer. It was small, so I took a photo and enlarged it to see the tell-tale nodes and pygidial ribs terminating right at the border. Yes, that is a Mystrocephala. It was in the same rock as all the other usual trilobite suspects, but I don't believe it is reported in this material, relegated as it is to the Amherstburg. This is yet another mystery that underlines the need for more sustained research in Ontario trilobites!