Playtceras spinosum gastropod on Arthrocantha crinoid calyx from Arkona

About three years ago I posted some pictures of a Platyceras sp. gastropod that was fossilized on top of an Arthrocantha sp. crinoid calyx that came from the Silica shale in Ohio. This past fall I found a similar fossil at a site near Arkona, Ontario, Canada. The specimen came from a weathering pile of Arkona shale (Devonian, Givetain stage) and was found on the surface.  The gastropod has a few circular openings on it's shell that I interpret as being the bases for spines so I should label it as Platyceras spinosum. Update 01/24/15 - thanks to the comments of a reader I was reminded that spiny specimens of the gatropod Platyceras are now called Spinyplatyceras arkonense.

 

There are a couple of bryozoan epibiont patches on the Platyceras shell as well but I am unsure of the species. Possibly Paleschara incrustans?