Ohio Trilobites

[FossilFrenzy]

I was given these two trilobites from my uncle in Michigan, and he found them locally in Ohio about 11 years ago. I was thinking they are flexicalymene but I am not certain since I am new to identification. 

Thanks in advance!

The smaller one is almost exactly 0.5" long (back of matrix shown), the wider one almost 1.5".

Edited December 26, 2018 by FossilFrenzy
Images out of order

[Kane]

The second one is a phacopidae. If found in Ohio, it is likely Eldredgeops sp. (possibly E. crassituberculata or E. rana). What makes this genus interesting apart from its iconic appearance is the presence of schizochroal eyes, inflated pustular glabella, and the fact that it lacks any facial sutures (the process of ecdysis involved a separation of the cephalon from the thoracopygon). 

[FossilFrenzy]

On 12/26/2018 at 10:53 AM, Kane said:

The second one is a phacopidae. If found in Ohio, it is likely Eldredgeops sp. (possibly E. crassituberculata or E. rana). What makes this genus interesting apart from its iconic appearance is the presence of schizochroal eyes, inflated pustular glabella, and the fact that it lacks any facial sutures (the process of ecdysis involved a separation of the cephalon from the thoracopygon). 

 

The second one meaning the wider one or the 0.5" one with better preservation?

I thought schizochroal eyes meant that they do have eye facets, is that correct? 

[Kane]

On 12/26/2018 at 10:51 AM, FossilFrenzy said:

 

 

 

 

This one.

Holochroal and abathochroal eyes also have lenses, but they are much smaller and harder to see even on well preserved examples. Here's a handy comparison of the three types of trilobite eye:

http://www.trilobites.info/eyes.htm

[piranha]

58 minutes ago, Kane said:

Holochroal and abathochroal eyes also have lenses, but they are much smaller and harder to see even on well preserved examples. Here's a handy comparison of the three types of trilobite eye: http://www.trilobites.info/eyes.htm

 

 

Although it has been generally accepted since Jell 1975, that there are three types of trilobite eyes, more recently it has been suggested that there are only two types of eyes; holochroal and schizochroal.  The abathochroal eye described only from eodiscid trilobites, is most likely a paedomorphic holochroal eye.

 

 

text from:

 

Zhang, X.G. & Clarkson, E.N.K. 2012
Phosphatized eodiscoid trilobites from the Cambrian of China.
Palaeontographica Abteilung A., 297(1-4):1-121   PDF LINK

 
The eyes of eodiscoids were described as abathochroal by JELL (1975b), who considered them to be distinct from holochroal eyes since the lenses were somewhat separated from one another, along with a summary that the eyes of eodiscoids resemble holochroal eyes in five respects, and there are eight differences from the schizochroal type. Of these, two key features for establishing these eyes as a separate type are the lenses not being in contact with any of the surrounding lenses, and each lens possessing its own corneal membrane. However, with more and more phospatized material being documented, and especially with the more fully detailed morphological examination of the visual surface of the eodiscid Pagetides, our new observations do not support the view that abathochroal eyes are distinct from the other two well-known types.
 
For instance, JELL (1975b) believed that each of the individual lenses carried its own corneal cap, but the fact that the outermost thin layer of the visual surface can flake off, taking with it many lenses together, rather than just a single one, casts doubt on this interpretation. Actually, the internal surfaces of some librigenae with the visual surface attached show that some of the fine lenses are polygonal in outline (Plate 16, Fig. 7), rather than circular as seen from the external surface. This is because these lenses remained in close contact as they grew towards a centre point of the visual system, and this has led to the deformation of the outline of lenses from circular to mostly hexagonal, as well as a few pentagonal and quadrilateral (also see ZHANG & CLARKSON 1990, pl. 2, figs 2-6). Moreover, it is now known that the juveniles of holochroal-eyed trilobites have separated lenses (CLARKSON & ZHANG 1991, CLARKSON & TAYLOR 1995), and that they are likewise separated in the paedomorphic Ctenopyge ceciliae (CLARKSON & AHLBERG 2002).
 
If eodiscoids are indeed paedomorphic derivatives of holochroal-eyed polymerid trilobites, is it not likely that they would have separated lenses too? It may be, therefore that the concept of abathochroal eyes as a separate eye type, though adopted earlier (CLARKSON 1997) is no longer sustainable, for the moment we leave the question open. In the descriptive part of the text, accordingly, we describe the eyes of eodiscids as abathochroal, because this term to date remains absolute as only known from eodiscoid trilobites.