Ok I know I'm slipping, first the Friday fossil then the weekly fossil now... the occasional fossil. Work with me people I'm still finding my pace. I think this is the second trilobite I've done but that's ok trilobites are cool. Above there's a slab with a bunch of trilobites, most of them are Elrathia kingi but if you look very carefully near the top and a little to the right (click on the picture to make it big) you'll see a little thing that looks like a fat figure 8, that's Peronopsis here's a close up of one of those.
Peronopsis is a blind trilobite (most trilobites had really wicked compound eyes) and it's planktonic which means it would just float in the water column. Elrathia is a very common triloite you frequently find them for sale. Many times they're missing a part called the free cheek which makes their heads (which are actually called cephalons.. at least I think that's the plural of cephalon.... cephala???) look squeezed, you can see this in some of the trilobites in the rock above. They're still Elrathia kingi they're just missing their free cheeks. As with many trilobites these are great index fossils, these are common in, and restricted to the Middle Cambrian. So if you find one you know how old the rock is. Very handy
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