Nautiloid

[Pippa]

Hello all, 

 

I don't know much about cephalopods and really could use your help.
I found this small rock with the tiny nautiloid specimen in the banks of the Rock River in Ogle county, Illinois. The area's bedrock is Middle Ordovician (Mohawkian, Ancell Group).

 

I believe it belongs to the order of the Actinoceridae. The "camerae" end in double pointed arches instead of a straight edge,  just as Wikpedia's illustration shows in the 2nd pic below.  

What seems to be unusual in my specimen - can't find any photos of this anywhere - are the rounded camerae, vs the tightly lined-up straight banding on other specimens.  (I'm not sure about the correct terminology...sorry).

 

If I'm not totally off base, is there a chance to narrow down the ID further? 

 

Thanks in advance.

 

 

General form of Actinocerid: 

 

 

 

[Manticocerasman]

all the cross sections of those chambers are inclined in the same direction, I'd rather think this specimen is a cross section of a gastropod.

 

 

[Ludwigia]

I agree with gastropod.

[BobWill]

I agree with gastropod.The drawing from Wikipedia shows an oblique view that makes the septa look inclined, but they're much straighter than that. Your fossil also has a greater apical angle than a cephalopod would.