I have a soft spot for large asaphids (who doesn't? LOL), and the ones that occur in the Aseri Formation in St Petersburg, Russia are quite stunning for their size and apparent simplicity, if not their variation. As time went on, and with more turbid seas, these asaphids started developing longer eye stalks, or peduncles, so that they could - like modern day crabs - keep themselves buried while only their eyes would be above the sediment on the look-out for predators or prey. I recently purchased a Asaphus kowalewskii a few months ago, which also represents pretty much the extent of eye stalk development.
(Photo credit: http://www.fossilmuseum.net/Fossil_Sites/trilobites-russia/rissian-asaphida-trilobite-evolutionary-sequences.htm)
Above you can see the evolutionary progression of the Russian asaphids. Arriving in the mail today were two more to add to the family:
This enrolled specimen is Asaphus cornutus. The rolled up appearance gives it a kind of "Kermit" like look. My forum friend Roger has an Isotelus gigas (also a related Ordovician asaphid) that he nicknames Kermit.
And this lovely and large prone is Asaphus punctatus. I'm pretty happy with these two new trilobites.