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This one has me stumped.  I think it is the body whorl of a gastropod (DSR, Middle Devonian, Hamilton Group, Moscow Fm., Windom Shale).  It is smashed, but the full circumference of the whorl is present, which means the aperture has to be on the left (which is consistent with the direction of the growth lines) (see arrow).  If that is the case, there should be a shallow furrow or ridge in the center of the whorl running parallel with the cords and perpendicular to the growth lines if it were something like Mourlonia or even a Bellarophontacea.  I see no evidence of such, not even on the crimped / folded / smashed edges above and below.  One would think that with such distinct surface detail that this one would be easy...  Any thoughts?  The fossil is about 46 mm in length.  Scale in mm.  @Jeffrey P, @Fossildude19, @Darktooth, @Kane

 

Here is outer side of the shell.

20200622_145104.jpg.62d3db4c8e57e63a3e1d9aee5fe3e3f1.jpg

 

Here is the shell flipped over to show the other side of the whorl.  I think the broken area on the right is where the body whorl continued to the second whorl (which is missing).

20200622_144957.jpg.c74c8a6db398113527a04d11317f6924.jpg

 

Here is both views side by side:

5ef15f12f1ef1_UnidentifiedMollusc.thumb.jpg.83a15fcc09b62342a5de6d2fab3510c5.jpg

 

Here is where I believe the aperture is located (I have prepped to the edge of the shell, and the shell ends there).

5ef15f18dccf5_UnidentifiedMollusc2.thumb.jpg.d4bb74f96f1aed9baf7ec3222c71efbc.jpg

 

 

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I am not sure about this, but I looked through the Linsley PDF and it has Platyceras undatum which looks very similar to your fossil here.

I don't think that name is still in use though as there are very few references to it elsewhere.

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24 minutes ago, Misha said:

I am not sure about this, but I looked through the Linsley PDF and it has Platyceras undatum which looks very similar to your fossil here.

I don't think that name is still in use though as there are very few references to it elsewhere.

Thanks, Misha.  I was looking at that one, too.  Unfortunately, Hall's (1879) description (Palaeontology of New York, Vol 5, Part 2) doesn't include the surface detail which was lacking in his specimen.  But a Platyceras would be a good possibility given the form of my fossil (i.e. the surface ornamentation is present on both sides of the body whorl - one would think that if the inner surface had been adjacent to a second whorl that it wouldn't have the crisp ornamentation that my specimen has).  Lindsley doesn't indicate whether P. "undatum" is known from Lower, Middle, or Upper Devonian.  I'm assuming early Devonian if Helderberg Group.

 

5ef16f4ba1664_Platycerasundatum.png.76265b1fa53844a07a0d10b43159ef5e.png

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8 minutes ago, Peat Burns said:

Thanks, Misha.  I was looking at that one, too.  Unfortunately, Hall's (1879) description (Palaeontology of New York, Vol 5, Part 2) doesn't include the surface detail which was lacking in his specimen.  But a Platyceras would be a good possibility given the form of my fossil (i.e. the surface ornamentation is present on both sides of the body whorl - one would think that if the inner surface had been adjacent to a second whorl that it wouldn't have the crisp ornamentation that my specimen has).  Lindsley doesn't indicate whether P. "undatum" is known from Lower, Middle, or Upper Devonian.  I'm assuming early Devonian if Helderberg Group.

 

5ef16f4ba1664_Platycerasundatum.png.76265b1fa53844a07a0d10b43159ef5e.png

Many of the Platyceras I have seen are quite similar in morphology to your piece. I think it is likely that this is a member of that genus or a related one as well. 

That one just happened to look very similar at first glance which is why I pointed it out

 

I am really interested in hearing what others will say about the fossil.

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