Very Fishy indeed... I don't think it to be a eurypterid, there are very clear scales present...ie piscean, no dermal chitinous plates dorsally. The fish is squashed in a dorso-ventral position, the large 'eye' like structures are the opercular plates, covering the gills, the left eye socket being just visible, forward of the plate?. Fleshy pectoral appendages!! but heavily scaled again...
Where did you find the fish? You say 290-250 MYA but then say you've collected from the 'Carb' beds...?
250-290 MYA is the Permian period, post Carboniferous, and the fishes to be expected are likely Palaeonisciformes, Acrolepsis and Platysoma types, Rhabdoderma types (Coelacanthids) and Elonicthyids, etc...?
Could it be from the Bude beds???
If so, then circa 316 MYA, Carboniferous (354-290MYA) - Possibly Cornuboniscus sp?
Doesnt seem to be like the placoderms (Ptericthyodes milleri et al) I have in my Devonian collections, from Achanarras and Spittal flagstones....Placoderms are just that, flat sheets of bony plates over the head and thorax and then a relatively exposed scaled tail.
Will be nice to see what the reaction is...I'll plump for a dorso-ventrally flattened
Cornuboniscus budensis... was going to say Rhabdoderma initially, but cannot see the giant scales about the head or the characteristic flame like patterns on the scaling that so defines them...