Simple Mid-Devonian ID?

[Kane]

Took advantage of a break from the early wintry weather to go play in my fossil pit out back (London, Ontario), and came upon this.

 

I'm sure this will be a cinch to identify, but i'm drawing a blank. It has ribbing reminiscent of an ammonite, but this was found in the Dundee Fm, Mid-Devonian, so too old for that. Ammonoids from around these parts don't tend to have ribbing like this, nor the appearance of nodes.

 

I was thinking some kind of coiling gastropod. Too large and flat to be a Paleozygopleurid. If it is a gastro, I know how tough they can be to identify from a steinkern, but I thought I'd give it a go. As I'm one of the few on here who have access to Dundee Fm deposits, perhaps it is reminiscent to a similar Devonian formation where one of you collects. Does this seem familiar to anyone?

 

Sadly, try as I might, I couldn't locate any other pieces from this rock, so this is all I have to go on. 

[Manticocerasman]

I wouldnt exclude cephalopod  check out Hercoceras and other Rutoceratidae.

 

[Kane]

15 minutes ago, Manticocerasman said:

I wouldnt exclude cephalopod  check out Hercoceras

Had a look, but only the nodes (and not the ribbing) seem there on Hercoceras... but, your suggestion led me surrepetitiously to this interesting paper. 

 

I think cephalopod is back on the table!

 

Image from:

Dzik, J., Korn W., and D. Korn (1992) Devonian ancestors of Nautilus. Palaont. Z. 66(1/2); 81-98

[Manticocerasman]

5 minutes ago, Kane said:

Had a look, but only the nodes (and not the ribbing) seem there on Hercoceras... but, your suggestion led me surrpetitiously to this interesting paper. 

 

Image from:

Dzik, J., Korn W., and D. Korn (1992) Devonian ancestors of Nautilus. Palaont. Z. 66(1/2); 81-98

 

Aaah Korn  perfect for paleozoic cephalopods 

 

 

[Jeffrey P]

I'm thinking cephalopod also. Prochorites- a Devonian goniatite, has both nodes and pronounced ribbing.