Lichid trilobite ID

[Paciphacops]

I recently found an exposure of the Ordovician Catheys formation in eastern Williamson County, TN. The exposure of blue-grey shaly limestone seems to match well with the trilobite rich facies described by Bassler in the Franklin, TN area. I did not get to hunt it very long, but saw lots of fossils and several trilobite fragments. In addition to many fragments of Isotelus, I found several fragments of lichid trilobites. Bassler referred to these as Platylichas sp. There is a lichid described from the somewhat younger Leipers formation, which Bassler referred to as Amphilichas halli (now considered Alolichas halli). He may have just used names from prior work, but he also may have seen some differences. These are definitely from the Catheys and not the Leipers, which is absent over the center of the Nashville dome. I do intend to go back soon and look for more, maybe even finding the elusive articulated specimen. I'm curious what distinguishes Alolichas from Platylichas, and what should I call these other than unknown lichid? Thanks.

[Paciphacops]

[Paciphacops]

[Paciphacops]

[Kane]

My first thought was Alolichas halli, too, but I don't seem to have a faunal list of the Catheys Fm on hand. I'd have to dig more into my materials, but I'm fairly certain @piranha will find it much faster than I can. 

 

That aside, very nice disarticulated finds of an uncommon lichid! 

[piranha]

Allolichas 1-3

 

 

Amphilichas cf. cornutus? @GerryK

[Paciphacops]

Thanks Piranha! I will label the first 3 as Alolichas sp. for now, and see what Gerry thinks about the last one. It would be nice if there is more than one species present. There are also supposed to be fragments of a large Acidaspis in these layers, at least at a section not too far away, but I did not find any (yet!). Bassler called it Acidaspis rebecca, but I don't think it was ever officially described.

[piranha]

Allolichas is the correct spelling.  I also contacted a friend who is a lichid specialist for another opinion.  I will post the response shortly.

[piranha]

My friend just replied.  Go ahead and label them all: Allolichas halli

 

 

"It’s not possible to give a reliable generic assignment on the basis of the fragmentary pygidium alone, but the presence of a pleural furrow on the third segment does not favour Amphilichas. However, since this pygidium is pretty obviously conspecific with the other specimens in your photos, Amphilichas can definitely be ruled out because the bullar lobe is not fused with L1, and the furrow bordering the bullar lobe posterolaterally appears to be S1 rather than the axial furrow (unfortunately, the cranidia are not shown in the best orientation – i.e. direct dorsal view). I agree that they look very much like Allolichas halli."