Decorah Shale Trilobite Cephalon???

[minnbuckeye 2,997]

Couldn't help myself yesterday and returned to an outcrop of the Decorah Shale, Ordovician in NE Iowa. Found many nice specimens.  (Adam, I may need to substitute some of my current finds with what is in your package) Here is something that perplexes me. I thought it was a partial trilobite cephalon/ genial spine but after looking at the species mentioned to occur in the formation, I struck out. Sooooo can anyone provide an identification? Thanks!!!!! 

 

 Mike 

 

  

 

 

[piranha 7,145]

Ceraurinus sp. is reported from the Decorah Shale:

 

[minnbuckeye 2,997]

@piranha, Thanks!! Initially I considered the possibility of Ceraurinus species but discounted it because of the pits in the preglabellar field/ eye?. I thought Ceraurinus had bumps. I have since looked at examples from the Decorah Shale and see none that have the tiny nodules all the way down the genial spine nor the pits.  I am still confused. 

 

Mike

[piranha 7,145]

2 hours ago, minnbuckeye said:

@piranha, Thanks!! Initially I considered the possibility of Ceraurinus species but discounted it because of the pits in the preglabellar field/ eye?. I thought Ceraurinus had bumps. I have since looked at examples from the Decorah Shale and see none that have the tiny nodules all the way down the genial spine nor the pits.  I am still confused.

 

Ceraurinus cheeks are pitted:

 

"Ornaments of a different type, consisting of perforations of the test, have been noted in several species. Rather large perforations extend through the cheek lobes in Ceraurinus,
Pseudosphaerexinella and Holia. These are of a type long known and described in many species of Ceraurus and Ceraurinus."

 

 

text from:

 

Evitt, William R. 1950

Trilobites from the Lower Lincolnshire Limestone near Strasburg, Shenandoah County, Virginia.

PhD Thesis, The Johns Hopkins University, 392 pp.

[minnbuckeye 2,997]

Thanks!

[GerryK 292]

The free cheek is large and the ornamentation is characteristic of Gabriceraurus herrmanni, which does occur in the Decorah.

[piranha 7,145]

39 minutes ago, GerryK said:

The free cheek is large and the ornamentation is characteristic of Gabriceraurus herrmanni, which does occur in the Decorah.

 

 

I looked at this one too quickly and did not account for the scale or the fact that is not a genal spine.  Gabriceraurus indeed!

[minnbuckeye 2,997]

@piranha, @GerryKYour help is appreciated. My confusion on ID was based on assuming the pointed end was in fact a genial spine. Now, knowing the  piece showing in the matrix is anatomically a free cheek, your suggestions make sense!!!!