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Analysis of fossil occurrences in late Osagean-early Meramecian stratotype beds of the upper Mississippi River Valley shows that major faunal changes occur within the Warsaw Formation, not at the underlying Keokuk-Warsaw formational contact where the Osagean-Meramecian serial boundary is presently placed. Relying on this evidence, we propose raising this boundary to the base of the informal upper Warsaw member described herein. The boundary is recognized by the first occurrence of the brachiopods Warsawia lateralis, Planalvus densa, Crossacanthia perlamellosa, Setigerites altonensis, and Tetracamera subcuneata, the blastoid Pentremites conoideus, and the calcareous foraminifer Globoendothyra baileyi. Use of these fossil appearances provides a more rigorous definition of the serial boundary and permits correlation beyond the Mississippi River Valley. Foraminifers suggest that the boundary falls within the middle Visean of western Europe. The stratotype section for the proposed boundary is located near the type locality of the Meramecian Series at Meramec Highlands, St. Louis County, Missouri. The lithostratigraphy of the late Osagean and early Meramecian is reviewed in key areas within the Mississippi River Valley and a new member, the Peerless Park, is proposed for a shoaling unit within the middle of the Keokuk Limestone.

The Yeyungou Formation near the town of Wushi on the north side of the Tarim Basin contains late Visean (Tulsky-early Aleksinsky) calcareous foraminifers, algae and incertae sedis deposited in mixed siliciclastic-carbonate lithologies within shelf and slope-to-basinal settings. Similarities with coeval assemblages found in middle and western Asia and on the Russian Platform confirm the relatively unrestricted biotic communication between continental plates across the Paleotethyan seaway at that time. The carbonates at Wushi are both in situ and reworked from the collapse of upslope platform beds. The latter are composed of shallow-shelf, grainsupported bioclastic lithologies and microbial-skeletal algae buildups that are widely developed on contemporaneous Paleotethyan platforms. Species described in this paper include the foraminifers Carbotarima postfinitima n. gen. n. sp., Mediocris? liae n. name and Pojarkovella wushiensis n. emend., and the alga Asteroaoujgalia gibshmanae n. gen. n. sp. The microbiota is fully illustrated.