Heterochrony is an important component of evolutionary change in the shell sculpture of turritelline gastropods from Paleocene and Eocene sediments of the Gulf and Atlantic Coastal Plains. A survey of heterochronic modes in these gastropods indicates that peramorphosis is dominant over paedomorphosis, a result counter to the pattern previously reported in gastropods and most other groups. Although lack of ontogenetic age data makes firm conclusions impossible at present, peramorphic patterns may have been produced by more than a single process. Possible explanations for the dominance of peramorphosis in the evolution of shell form in this group include a bigger role for intrinsic constraint in controlling shell form versus soft-part anatomy, selection for larger shell size, and the chance discovery of only peramorphosis in this study.

The tricranoclad demosponge Hindia sphaeroidalis Duncan, 1879, is reported as a common silicified sponge in the basal dolomite of the Deep Lakes Member of the Upper Ordovician Fish Haven Formation of northeastern Utah for the first time. A small juvenile orchoclad anthaspidellid, Hudsonospongia? sp., is also the first of that family reported from Fish Haven beds and the Deep Lakes Member. Both taxa are from localities on the eastern slope of Mount Magog, north of Tony Grove Lake, in the Bear River Range, Cache County, east of Logan, Utah.

The enigmatic tabulate genus Palaeacis is composed primarily of species with wedge-shaped coralla. Palaeacis walcotti Moore and Jeffords, 1945, P. kingi Jeffords, 1955, and P. cf. P. walcotti, described below from the Morrowan (Pennsylvanian) Golf Course Formation of the Ardmore Basin, south-central Oklahoma, represent a distinctive morphogroup characterized by a discoid corallum. Discoid Palaeacis ranges from the Morrowan to the Missourian and, so far, is known only from the mid-continent region of North America. The discoid shape, combined with concentric skeletal accretion, large corallite diameters, complex calice floors, and porous skeleton suggest, based on comparisons with the functional morphology of recent scleractinians, that these corals were well suited to an auto-mobile (vagile) life strategy, much as are many Recent fungiid corals. Discoid Palaeacis inhabited environments with muddy or sandy, unconsolidated substrates and was associated with low-diversity, nonencrusting faunas. This association is consistent with an auto-mobile life strategy. Auto-mobility in Palaeacis would represent the first such reported occurrence in the Tabulata, and the first in Paleozoic colonial corals of all types.

Gastropods are abundant in the Middle Ordovician (Whiterockian) Antelope Valley Formation of Nevada. Because Whiterockian rocks are absent in much of central and eastern North America, these Nevada gastropods play a significant role in understanding the Early to Middle Ordovician transition of the class. The shell and operculum of a new genus and species of macluritoid, Monitorella auricula, is described. New euomphaloid taxa include Walcottoma frydai n. gen. and sp., Rossospira harrisae n. gen. and sp., Barnesella measuresae n. sp., Helicotoma gubanovi n. sp., Lytospira yochelsoni n. sp., and Malayaspira hintzei n. sp.

The ontogenies of Prorensselaeria and Nanothyris, described here for the first time, suggest that Cloud's Dielasmatidae are closely affiliated phylogenetically with Cloud's Centronellidae. This is based on the fact that the type species of Nanothyris goes through an initial mutationellinid (Cloud's Dielasmatidae) growth stage before reaching its adult rensselaerinid (Centronellidae) growth stage. The ontogeny of Prorensselaeria requires that it be transferred from the Globithyrinae (Rhipidothyrididae) to the Mutationellinae (Meganteridae [=Cloud's Dielasmatidae = Stehli's Mutationellidae]). Further consideration of their ontogenies permits the transfer of Meganteris, Meganterella, and Reeftonella to the Meganterinae of the Meganteridae. It is recommended, because of the placement of Meganteris in the Meganterinae, that the term Meganteridae replace Mutationellidae, and Mutationellinae be restricted to costate Meganteridae. The subfamily Adreninae of the Meganteridae (=Stehli's Mutationellidae) is proposed to include Adrenia, Cydimia, Micidus, Sturtella, Barbarothyris, and Lingshanella.

The information developed here permits one to conclude that there are two kinds of families: 1) those generated by directional selection, involving major adaptive radiations, the type generated by quantum evolution in Simpson's sense; and 2) those generated by minor developmental changes, that do not involve major adaptive radiations, although they do result in morphological and biogeographical differences great enough to warrant the erection of families.

Bimuropora dendroidea, previously assigned to other genera, is described from Tennessee and B. winchelli is reported from Nevada. The occurrence of B. winchelli in Nevada extends the geographic range of the Middle Ordovician trepostome genus Bimuropora in North America. These two species share many derived characteristics with the halloporids, including a similar growth pattern and fluted zooecial walls in the endozone. This strengthens the hypothesis that the bimuroporids are a sister group to the halloporids. Sonninopora, a monospecific genus, contains these same features, and because of the presence of acanthostyles it is removed from the family Halloporidae and assigned to the family Bimuroporidae.

The brachiopod genus Verneuilia Hall and Clarke, 1893, is recognized for the first time in North America, where it is represented by a new species described here, V. langenstrasseni. This occurrence not only extends the geographic range of the genus, but also the lower age and stratigraphic limit into the Eifelian (early Middle Devonian). Previously, the oldest known species was the type, V. cheiropteryx d'Archiac and de Verneuil, 1842, from the Givetian (late Middle Devonian) of Germany. Internal structures of V. langenstrasseni n. sp. are similar to those of genera in the ambocoeliid subfamily Rhynchospiriferinae, providing the first good evidence of a systematic relationship.

The systematics of vermetid gastropods is in a shambles, with few genera defined by valid autapomorphic characters. Heretofore, the genus Petaloconchus has been included among the few adequately characterized groups, thanks to possession of a double internal lamina on the middle whorls. Yet abundant anecdotal information has been available for 100 years on the absence of laminae in high percentages of individuals within samples, and in entire populations that must be placed within the genealogical nexus of Petaloconchus. I demonstrate that such a nonlaminate population exists within the very material used to define the type species of the genus, Pliocene Petaloconchus sculpturatus Lea, 1843, from the Gulf and Atlantic Coastal Plain of the United States. I use X-radiography and multivariate biometry to show that this population from the Pliocene Jackson Bluff Formation at Jackson Bluff, Florida, is fully alaminate, but otherwise indistinguishable from P. sculpturatus. After considering a range of solutions, I name this population as a new subspecies, Petaloconchus sculpturatus alaminatus. I discuss theoretical and practical issues arising from populations that lack the defining feature of their genus.

The Wenonah Formation of New Jersey yields an ammonite fauna comprising Menuites portlocki (Sharpe, 1855), Placenticeras placenta (DeKay, 1828), P. minor n. sp., Nostoceras (Nostoceras) puzosiforme n. sp., Nostoceras (Nostoceras) aff. N. colubriformis Stephenson, 1941, Didymoceras n. sp., Didymoceras spp., Parasolenoceras sp., Baculites cf. B. scotti Cobban, 1958, Baculites sp., and Trachyscaphites pulcherrimus (Roemer, 1841). Although commonly regarded as lower Maastrichtian by micropaleontologists, the presence of M. portlocki and T. pulcherrimus is an indicator of upper, but not uppermost, Campanian in a northwest European sense, and the presence of Baculites cf. B. scotti suggests uppermost middle Campanian in terms of the Western Interior provincial substages.

In a large collection of Wenlockian gastropods from north Siberia, a single small specimen shows the operculum in situ just within the aperture. In other morphologic features, particularly the presence of numerous spiral lirae on the shell, this species is similar to Silurian gastropods traditionally assigned to Oriostoma. Preservation of the operculum is far from perfect, but almost certainly it has paucispiral growth, rather than concentric or multispiral construction. This new species (Australonema varvarae n. sp.) is assigned to Australonema, previously known only from the Lower Devonian of Australia, primarily because of the form of the operculum. The material was obtained from just below a biostromal unit in a bed interpreted as an interreef lagoon in an area of locally relatively quiet water.

Part and counterpart of a well-preserved specimen of Gondekia lancifer (Reimann, 1945a), and a well-preserved specimen of Pseudohydnoceras erraticum Reimann, 1935, are described from the Wanakah Member of the Middle Devonian, Givetian, Ludlowville Formation, of western New York State. The specimen of Gondekia is only the second articulated specimen known and is more complete than the holotype. It has an intact skeleton of felted sexiradiates of three orders of spicules; the largest has rays approximately 2 mm long. The specimen of Pseudohydnoceras has preserved hexactine-based spicules in a dictyid skeleton, described for the species for the first time.

It has been proposed previously that the northern Mississippi Valley Sunwaptan trilobite genus Dikelocephalus comprises 26 species. Morphometric analyses demonstrate that many of the criteria that had been used to define species of Dikelocephalus are invalid and additional analysis of biostratigraphically and biogeographically constrained collections is necessary before the taxonomic status of Dikelocephalus can be fully resolved. Our results indicate that infrageneric morphological variation in Dikelocephalus is continuous and lacks gaps that could be the basis for establishing multiple species. Many of the characters shown to be taxonomically insignificant in Dikelocephalus are also widely used in the definition of other trilobite taxa. This suggests that the species-level taxonomy of many trilobites may be substantially oversplit. Recognition of widespread oversplitting will have important consequences for biostratigraphic zonations, paleogeographic distributions, and estimates of taxonomic diversity.

Representatives of the ancestral cyclolobin ammonoid Demarezites Ruzhencev (Cyclolobidae) are known from only a few localities in North America where they occur as rare faunal elements. Demarezites furnishi n. sp. is based on a single specimen from “Middle” Permian (Roadian) strata in the Meade Peak Member of the Phosphoria Formation in eastern Idaho. Several specimens of the closely comparable Demarezites n. sp., described herein, are known from the Pipeline Shale Member of the Brushy Canyon Formation in West Texas.

Silicified and well-preserved specimens of the new orchocladine anthaspidellid genus and species, Virgaspongia ichnata, the rhizomorine haplistiid, Haplistion sphaericum Finks, 1960, and various root tufts, and the new hexactinellid species Steioderma hadra are reported from the Brentwood Member of the Morrowan Bloyd Formation from the Sulphur City quadrangle, in the Ozark Mountains of northwestern Arkansas. Virgaspongia is a subcylindrical branched or unbranched sponge that lacks a spongocoel and has a dendroclone-based skeleton in which trabs diverge upward and outward from an axial region. It is abundant here but is one of only a few anthaspidellid genera known from the Pennsylvanian. This is the first record of Haplistion from Pennsylvanian rocks of Arkansas, although the genus is widespread in upper Paleozoic rocks. The new hexactinellid species, Stioderma hadra, also documents the first occurrence of that genus from Arkansas and in Morrowan rocks. Only fragments were recovered but the swollen grotesque spicules, of several sizes, that make the fused dermal layer and outer sponge wall are distinctive, particularly where combined with an inner layer(?) or root tuft of monaxons of various sizes. Two different root tufts and one demosponge wall fragment(?) also occur in the collection.

The ostracode assemblage of the Arkadelphia Formation, upper Maastrichtian, of southwestern Arkansas is characterized by a well-preserved, relatively diverse, and abundant fauna representing 36 podocopid species and an undetermined number of species of the platycopid genus Cytherella. Thirteen of these account for 85 percent of the fauna. The dominant forms are Cytherella spp., Brachycythere rhomboidalis (Berry, 1925), Haplocytheridea renfroensis Crane, 1965, Haplocytheridea bruceclarki (Israelsky, 1929), and Brachycythere ovata (Berry, 1925), which account for about 57 percent of the specimens found. Other species that are less common, but are characteristic of the Arkadelphia, are Antibythocypris macropora (Alexander, 1929), Ascetoleberis hazardi (Israelsky, 1929), Aversovalva fossata (Skinner, 1956), Brachycythere ledaforma (Israelsky, 1929), Curfsina communis (Israelsky, 1929), Cytheromorpha arbenzi (Skinner, 1956), Escharacytheridea micropunctata (Alexander, 1929), and Veenia arachoides (Berry, 1925). The ostracode assemblage indicates that the Arkadelphia was deposited in the inner sublittoral zone.

The species Veenia parallelopora (Alexander, 1929) and Brachycythere foraminosa Alexander, 1934, are restricted to the Arkadelphia Formation and allow correlation with other Gulf Coastal Plain Upper Cretaceous units. A new ostracode interval zone, the Veenia parallelopora Zone, is proposed. This zone divides the Platycosta lixula Zone.

Calcareous planktic microfossils reported from the Arkadelphia and its correlatives in the Veenia parallelopora Zone indicate that these deposits are late Maastrichtian in age, not middle Maastrichtian as some authors have thought.

Colonies of the runner-like bryozoans Corynotrypa delicatula (James) and C. inflata (Hall) are common encrusters of Middle and Upper Ordovician shells and hardgrounds, especially in Cincinnatian deposits. The simplicity of their zooids contrasts with complexities in the dynamics of colonial organization. Both species have uniserial branches that bifurcate at intervals and, in addition, give rise periodically to lateral ramifications. Although angles of bifurcation and lateral ramification each average about 80°, bifurcations and lateral ramifications are fundamentally different modes of branch multiplication. In C. delicatula new lateral branches have conspicuous secondary zones of astogenetic change distinguished by elongation of successively budded zooids. Unlike bifurcations, the first zooids in lateral branches in Corynotrypa are not linked to the parent branch by a narrow basal canal, and each new lateral branch can be regarded as a distinct subcolonial unit. The ancestrula, described here for the first time in an Ordovician species of Corynotrypa, has a poorly differentiated protoecium and initiates a primary zone of astogenetic change. Colony growth in Corynotrypa was more plastic than in many other bryozoan runners. The systematics of C. delicatula and C. inflata are revised, and a lectotype is chosen for the former species.

A new brachiopod genus Cooperrhynchia is described for the species originally designated “Rhynchonella” schucherti Stanton, 1895, from the so-called Knoxville beds of northern California. A lectotype is selected for Cooperrhynchia schucherti (Stanton). An isolated carbonate lens within deep-water turbidites of the Great Valley Group (Jurassic–Cretaceous) yielded the brachiopod fossils near the town of Paskenta, western Sacramento Valley. The associated bivalve fauna indicates a mid late Tithonian age for the locality. Mollusks and the rhynchonellids Cooperrhynchia and Peregrinella are known from several scattered limestone lenses within Great Valley strata; collectively, these faunas and carbonate patches represent cold seep-associations that developed in forearc basins along the tectonically active northeast Pacific convergent margin during the late Mesozoic.

Recently developed analytical procedures for meshwork fenestrate and pinnate bryozoans made it possible to recognize two Russian species in the Toroweap Formation of southern Nevada. This analysis separates zoarial and zooecial features and emphasizes the three-dimensional form and size of the zooecial chamber as well as accessory features. In this investigation, these analytical procedures are successful even when specimens are fragmented and embedded in a hard rock matrix.

The bryozoans in the Toroweap Formation in this study were found to be more similar to Permian species of the Russian platform than to species described in earlier North American Permian studies. Five species of fenestrate bryozoans are present in the Toroweap Formation. Wjatkella permiana Morozova, 1970, and Polypora sargaensis Trizna, 1948, originally described in Russia, are recognized in the Toroweap. Three new species, Penniretepora oppositus n. sp., Septopora bilateralis n. sp., and Reteporidra anaphora n. sp., are present and, along with the Russian species, are described in this paper.

The local range zones of the five species of fenestrates were identified in three measured sections. Penniretepora oppositus and Septopora bilateralis are present throughout the three sections; Reteporidra anaphora is present in the lower two-thirds of the three sections; Wjatkella permiana is present in the middle parts of the three sections; and Polypora sargaensis is present in the upper parts of the three sections. Concurrent range zones, based on ramose bryozoans, were previously identified in two of the three sections and, using the distribution of the fenestrates in these two sections, four of the five concurrent range zones were recognized in the third section.

Description of two new specimens of Macroscenella superba (Billings) provides additional data on this rare, poorly known Paleozoic genus. Macroscenella was considered first to be a gastropod, then a monoplacophoran, and finally a coelenterate. Chondrophorine affinities for this form cannot be totally ruled out, but the new specimens increase the probability that it is a mollusk. If so, Macroscenella is more likely a patellacean gastropod than a member of any other group of the Mollusca, though evidence for placement within the Mollusca is equivocal; the interior of the specimens is not exposed and musculature is unknown. If the integument was a shell, it was thin.

Three new species of trilobites, Erixanium lacunatum, Cernuolimbus monilis, and Anechocephalus aphelodermus, have been recovered from two new fossiliferous localities in the normally unfossiliferous Collier Shale in the Ouachita Mountains of west-central Arkansas. These new taxa occur with other trilobites previously reported from the Elvinia Zone in the Collier and elsewhere. Like the other trilobites reported from the Collier, these new taxa were originally deposited on the outer shelf, and were later eroded and redeposited in the adjacent, deep-water basin. Other species assigned to these genera have also been reported from outer shelf or continental slope sites. Species of Erixanium were widely distributed in equatorial and subtropical paleolatitudes in the Late Cambrian.