Carboniferous Cephalopod ID, Solenocheilus or Ephippioceras

[cngodles]

To continue discussion on the specimen listed here, with renewed focus on it being a Cephalopod.

 

As of right now, I'm deciding between Solenocheilus and Ephippioceras. 

 

Going directly by the book: Index Fossils of North America (1944, 1980 printing), I can see positives for both.

 

Solenocheilus

(Lower Mississippian to Lower Permian, IN, IL, MO, KS, TX and Europe)

 

Recommended by a local expert, but doesn't specialize in Cephalopods.

 

Ephippioceras

(Mississippian in Europe, Pennsylvanian, Ohio to Kentucky, Nebraska to Texas)

 

The raised line along the midline of the plate photo is what is selling me on this one. My specimen is much larger than the plate, but not quite double the size.

 

 

 

So, two new photos of the specimen.

 

First, looking at the line:

(After seeing it this way, I was looking at it 90 degrees in the wrong direction)

 

Flipped, End over end.

 

 

So, any opinions? I was thinking of removing more matrix from the matrix heavy size, but it will certainly remove the shell material and leave the steinkern.

 

[cngodles]

This entry from the The Pennsylvanian Atlas of Ancient Life is pretty convincing to me concerning Ephippioceras.

 

https://pennsylvanianatlas.org/species/ephippioceras-ferratum/

 

 

 

 

 

[cngodles]

I have a second expert opinion on this being Solenocheilus. There goes my opinion. 

 

From the expert: The specimen is mostly a body chamber fragment with some traces of the septate phragmocone. It looks to me like a Solenocheilus. Very few coiled nautiloid genera get that size - some Solenocheilus I have seen are nearly 10 inchs wide and 12 inched in diameter.

[howard_l]

The best identification for Solenocheilus.is the location of the siphuncle which is located on the venter part of the shell, one of the only nautiloid this occurs in. 

[cngodles]

One final post on this, as I am settled on Solenocheilus. I removed most of the rock matrix from around the phragmacone. Here are a few rotated views of the top and bottom. I feel like the phragmacone was collapsed a bit upon burial. There were two separate shell layers a bit sandwiched. I did not remove the shell material from the phragmacone because I rarely get it to stay when I removed it anyway. Removing it may have exposed the suture line.

 

 

And a simple head on of the front: