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I have seven specimens of these, all with the same appearance and strange internal structure. They have perplexed me for years though I'm familiar with most fossils from the area. (I originally had three and have recently collected four more which enables them to be characterised more reliably. Altogether, five individuals are fairly complete). One small exposure of marine shale, Mississippian, Brigantian Stage, northern England, Co. Durham. The main features are: 1) See photos 3 & 4 -The shell material is strange, being irregularly honeycombed, resulting in a granular apperarance on the surface. I haven't seen any other shells at all like this from the same beds - brachiopods and bivalves being common. 2)They're roughly semicircular and shell-like. They very possibly have been paired down the straight edge. (Two of my seven specimens each consist of two disarticulated individuals, one on top of the other.) Bilaterally symmetrical, with a central sulcus or ridge. 3)The straight edge is thin and bent over. Where preserved it terminates with distinctive sharply curved ridged ornament. 4)They're all about the same size, 35-45mm across, and seem to be about 1mm thick. Although superficially brachiopod like, there's no sign of a hinge or umbo, and the texture isn't like any brachiopod I know. The fine structure closely resembles Jurassic ammonite aptychi of Laevaptychus type so aptychus is one possibility I've been considering though the shape doesn't match any I've found. Also, they're really quite common in the small source exposure whilst cephalopods are scarce (just one small orthocone to date). And Palaeozoic aptychi are generally rare and would be surprising. I have a few other ideas but will see what people can come up with. I hope it's obvious to someone! Here are four specimens, two of them being the possibly associated pairs. Thank you for looking! Specimen 1, paired: Specimen 1, top member removed (it broke off when drying!): Specimen two, worn fragment showing honeycombed internal structure. (All the specimens show this.) Specimen 2, closeup: Specimen 1, edge detail: Specimen 3, paired, partial at bottom overlaying complete one. Note close similarity of edge with previous photo (specimen 1) Specimen 4, with better preserved circular edge: EDIT: All seven specimens so far collected, in the same orientation to show their morphological consistency.

After the last one (link here: fish skull ) turned out to be a nice skull, I'm wondering if anyone could ID this bit? It's very 3D and hard to photograph without image stacking so I've given three views. Phosphatic nodule, Brigantian (U. Mississippian) marine shale, Co. Durham, UK. counterpart:

Anyone recognise this? Phosphatic nodule, Brigantian (U. Mississippian) marine shale, Co. Durham, UK. Nodules from this bed often contain fish bits, as well as cephalopods, inarticulate brachiopods and (rare) conulariids. Not cleanly broken but the shape is ringing a bell... concave counterpart

This is a scarce crinoid in the Mississippian of my area, usually found here as isolated columnals (and never articulated). So I was pleased to find this group yesterday on my first 2020 trip to a favourite locality in the Durham Dales. Needs a bit of TLC and probably light air abrading (it's fragile) but not bad for a quick brush and rinse. Mississippian, Brigantian, Three Yard Limestone (shale parting), Co. Durham, NE England.

I was surprised to see this specimen for auction and pleased to win it. It's Anguloserra thomasi, a rare tooth from an ophiocistioid echinoderm and comes from the same locality as the holotype described here (abstract only): Haude & Langenstrassen 1976. I've been interested in these since finding three similar specimens in the UK that took a while to identify - shown in the next post. It's preserved as an impression - most material in this matrix is decalcified. Carboniferous, upper Mississippian, Culm beds (equivalent of Brigantian and Arnsbergian beds in UK), Aprath, Germany. Scale in mm. Here's the holotype from the linked paper (a latex cast):

A while ago, I was convinced that this was an orthocone with possible sponge borings though it was never really resolved. http://www.thefossilforum.com/index.php?/topic/77979-strange-infestation-on-orthocone-shell-mississipian-ne-england/& @Al Dente suggested eurypterid as a possibility which I argued against, largely because they've never been found around here. However, a friend of mine has now found some undoubted eurypterid fragments in equivalent beds in Scotland, 120 miles away or so and where the faunas have much in common. He's pretty sure that this is indeed eurypterid (based on just a couple of closeup photos). I'm rather hoping it is though the boring sponge is also pretty interesting. Searching throws up Adelophthalmus as a distinct possibility, based on the ornament (see reference and drawing at the bottom of the post). So here it is again - eurypterid or bored orthocone? Brigantian (Mississippian) marine shale, Co. Durham, NE England. (Many more photos on the original thread, including very close up. The little rings are preserved in solid pyrite and go right through the shell/carapace.) From this paper on Pennsylvanian Adelophthalmus https://www.foss-rec.net/8/3/2005/fr-8-3-2005.pdf