Limestones of Silurian age (late Llandovery–Ludlow) from the Heceta Formation of southeastern Alaska (Alexander terrane) yield a diverse assemblage of calcified microbial organisms. Fourteen taxa are described, including the cyanobacteria Girvanella and ?Hedstroemia, possible cyanobacteria Epiphyton, Ludlovia, and Renalcis, three species of “Solenopora,” and microproblematica Rothpletzella and Wetheredella. Diagnoses and descriptions are also given of the new epiphytacean genus Hecetaphyton n. gen. and new microproblematica genera Tuxekanella n. gen. and Sphaerina n. gen.

A single specimen of the new dictyonine hexactinellid species Verrucocoelia biswasi was collected from the Middle Eocene Fulra Limestone from Lakhpat Fort, Kutch, western India. The euretoid species is broadly bowl-shaped, 7–8 cm wide and 5–6 cm high, with walls of branched to weakly anastomosed tubes that extend upward and outward from a simple, unfluted, walled spongocoel. Skeletal strands diverge upward and outward from near the gastral surface of each tube. The sponge occurs in silty tan marl with abundant alveolinids and less common other large foraminifera, bivalves, and gastropods in sediments thought to have accumulated in a quiet, sheltered environment, possibly a lagoon.

The Chesterian Imo Formation of northern Arkansas represents the highest Mississippian strata present on the Ozark platform and contains a unique, although sparse, coral fauna that is transitional between Mississippian and Pennsylvanian assemblages. Of the four most abundant genera represented, Lophophyllidium, Bradyphyllum, and Tectamichelinia are characteristic of Pennsylvanian assemblages and only Amplexizaphrentis is a typical Mississippian form. The fauna is interpreted as part of a shallow-water, muddy bottom community. Of the 11 rugosans and single tabulate coral described, the following are new: Bradyphyllum lesliense n. sp., Amplexizaphrentis maneri n. sp., Lophophyllidium imoense n. sp., and Tectamichelinia mangeri n. gen. and sp.

An abundant, varied, and well-preserved assemblage of discrete sponge spicules of late Ordovician age is described from the Malongulli Formation of central New South Wales. It is associated with one of the most diverse Ordovician siliceous sponge faunas known. The assemblage occurs in allochthonous limestone blocks within breccia deposits of a predominantly graptolitic and spiculitic siltstone succession, and is composed mainly of hexactinellid spicule types. Included are a number of distinctive forms, recognized as new taxa—Silicunculus bengtsoni, Kometia cruciformis, Chelispongia prima, and Pseudolancicula exigua. All are new genera except Silicunculus Bengtson, 1986, which was previously described from the upper Cambrian of Queensland. The problematical Anomaloides reticulatus Ulrich, 1878, is reported for the first time from Australia. A wide variety of other diagnostic, but more generalized, spicule types also occurs, including stauractines, pinnular and nonpinnular pentactines and hexactines, ornamented oxyhexasters and echinhexasters, clavules, anchorate root-tufts, and uncinates. The pinnular pentactines may be assigned to the form genus Palaeorubus Ishiga (in Ishiga et al., 1987), interpreted incorrectly by Ishiga as a radiolarian. The sponges, discrete spicules, and radiolarians of these limestone clasts were transported in debris flows to a basinal setting from peri-platform oozes that formed on the flanks of the shallow offshore island-arc platform of the Molong High.

Silurian calcareous algae, cyanobacteria, and microproblematica are abundantly preserved in the Alexander terrane of southeastern Alaska. They represent a diverse population of calcified microbes that contributed to the formation of a variety of shallow- and deep-water carbonate deposits. Five associations are recognized on the basis of recurring groups of microbial taxa. These include a Girvanella-Tuxekanella association that formed oncoids and thick encrustations on skeletal grains in shelf environments. A Renalcis association predominated in a stromatoporoid-coral reef that developed at the incipient shelf margin on a crinoid-solenoporid shoal (“Solenopora” association). Other organic buildups are characterized by a Ludlovia association, which constructed skeletal stromatolite reefs, and by an Epiphyton-Sphaerina association that contributed to the formation of a stromatolitic mud mound. A mixed microbial assemblage reflects transport and mixing of shallow-water microbial biotas that were deposited by turbidity currents, debris flows, and slumps in a slope environment.

Reticulate Hornera reteramae (Bryozoa, order Cyclostomata) have been discovered as free-lying, lyre-shaped colonies in the Castle Hayne Limestone (Eocene) in North Carolina. These specimens represent a striking instance of homeomorphy in colony form with the Late Mississippian genera Lyropora and Lyroporella of the order Fenestrata.

Bryozoans with reticulate growth habit most commonly develop upright colonies. Living representatives generally grow in quiet environments or microenvironments, and fossils are generally found in situ in quiet-water deposits. However, lyre-shaped Hornera reteramae occur in skeletal packstones inferred to have been deposited in a moderate-energy, shallow, open shelf environment near normal wave base. Upper Mississippian lyre-shaped colonies are preserved in skeletal packstones and grainstones in localized channels or on upper surfaces of low-angle cross-bedded sheets interpreted as high-energy, marine shoal deposits. Modification of the reticulate growth habit to low, peripherally weighted, free-lying structures apparently allowed invasion of higher energy sand bottoms, both in Mississippian and Eocene times.

Muscle scars are described for the first time in the Ordovician bellerophontoidean gastropod Carinaropsis Hall. Silica replicas from the Cannon Limestone of Tennessee preserve a pair of muscle scars, with a single elongate scar located on each umbilico-lateral angulation of the shell interior more than half a whorl back from the apertural margin. The scars are similar in general shape and position to muscle scars described in Bellerophon de Montfort and the pleurotomarioidean Porcellia woodwardi (Sowerby). In addition to supporting the soft parts within the widely expanded shell, the characteristic internal septum of Carinaropsis probably facilitated clamping of the shell aperture against the substrate.

A new gastropod genus, Dutrochus, is established for members of the family Microdomatidae that are characterized by a reticulate ornament of spiral cords and intersecting, finer collabral threads, with all but one spiral cord being of nearly equal strength, and the single remaining cord being of stronger (nearly twice the order) magnitude and being situated at the periphery. It is represented by the type and only known species, Dutrochus alaskensis n. gen. and sp., from the upper part (lower Middle Devonian; lower Eifelian) of the Lower? and Middle Devonian Cheeneetnuk Limestone, McGrath A-5 quadrangle, west-central Alaska. The genus is very close and nearly homeomorphic to the Permian microdomatid genus Glyptospira, but differs from the latter in possessing an extremely strong, peripheral spiral cord and an extremely thick, multi-layered apertural margin.