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Just a note that James Cullison's 1944 monograph on the rocks and fauna of the upper Lower Ordovician of Missouri and Arkansas is now freely available for download or perusal at https://archive.org/details/paper-cullison-1944-the-stratigraphy-of-some-lower-ordovician-formations-of-the This publication has always been devilishly tough to get a hold of. A nice systematic paleontology section deals with the many gastropods and other mollusks as well as the less diverse brachiopods, trilobites, and sponges. The monograph covers the following formations as currently accepted in Missouri: • Smithville Formation • Powell Formation • Cotter Formation • Jefferson City Formation Enjoy and share as you like. Full citation: J. S. Cullison, 1944: "The Stratigraphy Of Some Lower Ordovician Formations Of The Ozark Uplift." The University of Missouri School of Mines and Metallurgy Bulletin Technical Series, Vol. 15, No. 2, 112 pp + 35 pl.
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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: