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Hi! I wanna classify about this trilobites plate. It from morocco. I think It is maybe Nileidae? please help me to classify this trilobites genus and species! Size of trilobites is 3.5~6cm.

A seemingly simple question seems to not have a simple answer. How many orders of trilobites are there? Not everyone agrees on the number but is there a number that is generally accepted by the experts? I have seen anywhere from 9-14 different orders. @piranha has 14 in this thread, Sam Gon III has 11 on his site and I have seen many other sites with different numbers. Which is most up to date? Thanks in advance for any feedback. I'm going to tag two resident trilobite experts ahead of time. @Kane @piranha That was more than one question but they're all in the same order. Or are they?

Looking for help with this Early Ordovician (Floian) trilobite from the Powell Dolostone of Arkansas, USA. The specimens (GRAY FIGURE below) were identified by Taylor (1968) as cf. Lannacus nericiensis Wiman, but that species (now a species of Megalaspides) doesn't seem like a great match, as the author notes in the paper. In fact, I'm not sure that proper Megalaspides even lived in North America. Last week, an Arkansan found another asaphide specimen (MAIZE AND BLUE FIGURE below) in these same rocks, which may or may not be the same species as the specimens described by Taylor. My question: Could these all be specimens of Isoteloides canalis? That species is already known from the Powell Dolostone in Missouri per Weller & St. Clair (1928) (as Isoteloides whitfieldi, now a subjective synonym of Isoteloides canalis). Or are these instead specimens of a distinct Powell asaphide, and if so, what genus & species? Thanks in advance. 1959 Treatise blurbs for Isoteloides and Megalaspides are in the BLACK AND WHITE FIGURE below. Here's Taylor (1968): https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=3056&context=jaas Here's Weller & St. Clair (1928): https://share.mo.gov/nr/mgs/MGSData/Books/Volumes/Geology of Ste. Genevieve County/V-022.pdf GRAY FIGURE: MAIZE AND BLUE FIGURE: BLACK AND WHITE FIGURE: