Trilobites assigned to 14 genera and 14 species are reported from basal part of the Deadwood Formation in the Black Hills of South Dakota. Six additional taxa are left in open nomenclature. One new species, Cedarina dakotaensis, is described. These trilobites are assigned to a new zone, the Cedarina dakotaensis Zone, named after the most abundant trilobite species.

Species of Cedarina and Modocia are the most abundant in the Cedarina dakotaensis Zone, accompanied by less common specimens of species of Arapahoia, Menomonia, Hardyoides, Welleraspis, Kormagnostus, and Kingstonia. Cedarina dakotaensis and Modocia centralis are the most abundant species in the nearshore sandstone lithofacies, whereas Arapahoia spatulata is the predominate taxon in the offshore limestone lithofacies.

The fauna of the Cedarina dakotaensis Zone (which lacks species of Cedaria) occupies the biostratigraphic interval of the traditional Cedaria Zone of the Marjuman Stage. Trilobites from the Cedarina dakotaensis Zone can be used to correlate the basal part of the Deadwood with coeval strata elsewhere in North America.

The extinction of the Olenellina on Laurentia can be located within centimeters in the C-shale or uppermost Combined Metals Limestone members of the Pioche Formation in eastern Nevada. Olenellid species diversity beneath the extinction boundary is not diminished. One of the richest Laurentian intervals for articulated olenellids is in the 50 centimeters of shale immediately below the extinction boundary at Ruin Wash. Additional morphological information about some of the species comes from a silicified fauna 1.8 m below the extinction boundary at Hidden Valley. The olenellid fauna from the 2-meter interval below the extinction boundary is described. Questions about current generic and subgeneric relationships are discussed. Among general observations, intraspecific variability unrelated to size or taphonomic effects is minimal for most species; at least two species may have been capable of enrollment; and visual surfaces of one species show no evidence of facets. New species include: Olenellus (Olenellus?) fowleri, Olenellus (Paedeumias) chiefensis, Olenellus (Paedeumias) terminatus, Bolbolenellus brevispinus, and Nephrolenellus geniculatus. Olenellus (Olenellus) gilberti Meek and Olenellus (Olenellus) howelli Meek are revised.

Three species of Karakaschiceras, K. attenuatus (Behrendsen, 1892), K. neumayri (Behrendsen, 1892), and K. lycoris (Leanza and Giovine, 1949), and one species of Neohoploceras, N. arnoldi (Pictet and Campiche, 1860), are described and figured from the Valanginian strata of the Neuquén basin in west-central Argentina. The large collection of fossils available for study shows wide intraspecific variation regarding ornament and whorl section in Karakaschiceras neumayri and Neohoploceras arnoldi, casting some doubts on the current systematics applied to species of these genera. The biostratigraphic position of the four species in the Neuquén basin corresponds to the Karakaschiceras attenuatus Subzone of the Olcostephanus atherstoni Zone. This subzone is correlated with the Mediterranean Karakaschiceras inostranzewi and Saynoceras verrucosum zones of Europe at the base of upper Valanginian sections.

Thirty-four species of trilobites belonging to 21 genera are recognized in the Albertella Biozone within the Grassy Spring Member (new name) of the Pioche Shale of southeastern Nevada. Genera include Pagetia, Poliella, Kootenia, Olenoides, Albertella, Albertellina, Albertelloides, Delamarella, Mexicaspis, Paralbertella, Ptarmiganoides, Ursinella, Zacanthoides?, Amecephalites, Mexicella, Nyella, Onchocephalites?, Pachyaspis, Panacus, Plagiura, and Volocephalina. Two new corynexochid genera and species, Delamarella brevispinaspis and Ursinella major, are described. The existing corynexochid genus Albertella is revised to include two new species, A. fritzi and A. highlandensis. A new species, Albertelloides kitai, is described. Two new ptychopariid genera, Amecephalites and Panacus, plus four new ptychopariid species, Amecephalites sundbergi, Mexicella granulata, Panacus palmeri, and Volocephalina variosa, are described and Nyella immoderata Palmer is revised. In addition, the Albertella Biozone is divided into three new subbiozones, the lower Albertellina aspinosa Subbiozone, the middle unnamed subbiozone, and the Albertella highlandensis Subbiozone.

A review of the Late Ordovician, chiefly mid-Ashgillian, to Early Silurian, Llandoverian, pentameroidean brachiopods, the Virgianidae, permits them to be assigned to three subfamilies (Virgianinae [10 genera assigned], Mariannaellinae [5 genera assigned], Pleurodiinae [2 genera assigned]). Diagnoses are presented for each subfamily, with comments on diagnostic characters for each genus and species. All the genera occur in what are interpreted to have been relatively low latitude, warm water environments in Arctic North America, northern Europe, northern Asia, central Asia and South China; the presence of Australian Ordovician virgianids is uncertain at this time. The mid-Ashgillian pentameroid adaptive radiation was followed by latest Ordovician mass extinction, subsequently surviving recovery and radiation in the middle-Late Llandovery. Silurian radiations convergently mimicked the Ordovician event in many respects.

A phylogenetic analysis was used to determine evolutionary relationships within the Early Cambrian superfamily Olenelloidea Walcott, 1890. Phylogenetic patterns within the suborder Olenellina Walcott, 1890, which contains the Olenelloidea and the Fallotaspidoidea Hupé, 1953, are also discussed. The Olenelloidea are monophyletic, and synapomorphies uniting them include the condition of the ocular lobes where they intersect the frontal lobe of the glabella, and the condition of the lateral margins of the glabellar lobes. In contrast, taxa formerly assigned to the Fallotaspidoidea are shown to represent a paraphyletic grade of several genera, some more closely related to the Olenelloidea, and some more closely related to the Redlichiina Richter, 1933. Seventy-nine exoskeletal characters were coded for 26 taxa within the Olenellina. These included 22 ingroup Olenelloidea and four outgroup taxa that have traditionally been assigned to the Fallotaspidoidea. When subjected to parsimony analysis these character data yielded a single most parsimonious cladogram that provides an hypothesis of relationship for the generic clades within the superfamily. Two new genera are recognized herein, Fritzolenellus and Lochmanolenellus. It has been argued that genetic flexibility was so great and trilobite morphology was so plastic in the Early Cambrian that suprageneric classification of Early Cambrian trilobites is precluded. Although levels of intraspecific variability may have been slightly higher in the Early Cambrian relative to the mid Paleozoic, based on the extent of polymorphic character codings, it was not so high as to obviate attempts at recovering phylogenetic structure in a major clade of Early Cambrian taxa. In addition, the consistency index recovered by this analysis is not unduly low for a phylogenetic database of this size. The phylogenetic analysis also has bearing on patterns of allometric heterochrony, which have often been held to be significant in Early Cambrian trilobites. The paedomorphic retention of advanced genal spines into the adult probably evolved at least four times. Three of the episodes can be best described as neoteny, the fourth, as progenesis. Finally, based on the phylogeny, it is likely that rates of speciation in trilobites may have been two to three times higher in the Early Cambrian than in the mid Paleozoic.

Hanburia gloriosa is probably blind, the smaller specimens having a forwardly expanding glabella with lateral lobes, and six (rarely five) thoracic segments; larger specimens have a parallel-sided glabella with faint traces of lateral lobes, and six, in one case seven, thoracic segments; pygidium equal in size to the cephalon. All specimens may be holaspid, the larger corynexochoid-like; however, the smaller ones are not like any known corynexochoid. Hanburia gloriosa is the rarest trilobite from the Stephen Formation. This species, and other rare but widely distributed Lower and Middle Cambrian species from deeper water faunas are all of uncertain affinities. They do not fit into the general picture of trilobite evolution, nor appear likely ancestors of shallow water species.

Superbly preserved specimens of Eucalyptocrinites tuberculatus from the Waldron Shale (Silurian, Wenlockian) of Indiana have been found with epibionts attached in living position to their stems. The rhynchonellid brachiopod Stegerhynchus indianense, the tabulate coral Favosites forbesi, the annelids? Spirorbis and Cornulites, bryozoans, and rarely the ichnogenus Tremichnus utilized living crinoids as secondary tiering surfaces. Crinozoans also attached to upright crinoid columns, and their holdfasts are the most abundant epibionts on pluricolumnals. Eucalyptocrinites crassus individuals contributed to the success of their epibionts by providing stable attachment surfaces elevated up to one meter above the sediment-water interface. Although crinoid-epibiont relationships are frequently blurred by taphonomic processes, articulated crinoid specimens and encrusters on pluricolumnals suggest that secondary tiering was a significant paleoecological element in the Waldron Shale.

In the Recent biota, species of the hipponicid gastropod genus Sabia that excavate characteristic pits on the outer surfaces of shells of reef-dwelling gastropods and hermit crabs occur only in the tropical Indo-West Pacific region and in adjacent warm-temperate parts of Japan and Australia. I report the discovery of Sabia pits in reef-associated gastropod shells from the Cercado (late Miocene) and Gurabo (early Pliocene) Formations of the Dominican Republic. The likely culprit was Hipponix otiosa Pilsbry and Johnson, 1917, a species here reassigned to Sabia Gray, 1840. Pliocene extinction, which was far more severe in the Caribbean and elsewhere in the western Atlantic than in the Indo-West Pacific, selectively eliminated Sabia and its commensalism from Atlantic reef ecosystems. This case is one of several examples indicating the vulnerability of specialized associations to extinction-causing disturbances.

Rare to abundant specimens of Moorites Coryell and Billings, 1932, and Discoidella Croneis and Gale, 1938, have been recovered from 13 Pennsylvanian stratigraphic units in the Appalachian basin. Eight species of Moorites, including the new species M. sturgeoni, M. ornatus, M. percultus, and M. erugatus, are recognized. Discoidella is represented by D. lingulata Cooper, 1946. Moorites hewetti Coryell and Billings, 1932, is recognized as the type species of Moorites. An ontogenetic series of M. percultus illustrates changes in shape and ornamentation. Increase in complexity of ornamentation from Lower to Upper Pennsylvanian provides a basis for specific identification.

An unusual, lichenoporid-like bryozoan colony from Mid-Silurian strata on Gotland is described as a new cystoporate, Inconobotopora lichenoporoides new genus and species; a poorly known form from the same area and approximate horizon is reclassified as Inconobotopora silurica (Hennig, 1906). Similarities in overall morphology, particularly flagged by the distinctive radial-disk construction, combine with geochronologic sequence to suggest the possibility of an evolutionary lineage from Ordovician Constellaria, through Silurian Inconobotopora, to Devonian Botryllopora, and perhaps even on to Cretaceous-Cenozoic-Recent Lichenopora (although this last extension is extremely difficult to demonstrate in the present state of knowledge).

The arthropod macrofauna from the Middle Member of the lithographic limestones of the Tlayúa Formation, in quarries at Tepexi, México, is comprised of marine and nonmarine components. Marine taxa include a new species of flabelliferid isopod, a new genus and species of an anomuran, and a new genus and species of a brachyuran crab. Remains of an arachnid and an odonate nymph represent nonmarine constituents. Previous paleoenvironmental interpretations of a restricted lagoon, with periodic episodes of marine and freshwater influences are consistent with the nature of the arthropod fauna. Isopod remains, represented only by corpses, that resemble modern ectoparasites of fishes suggest that they are directly associated with the abundant fish remains found in the quarries, either as ectoparasites that released their hosts before they died or possibly as scavengers that fed on fish remains. The next most abundant arthropods are the crabs, most of which are corpses, suggesting that this group lived in or very near to the depositional site of the Tlayúa Formation. Based upon the new fossil material, the stratigraphic range for the Aeglidae has been extended to span Albian to Holocene time. Extant representatives of this family inhabit fresh water environments of South America.

An exceptionally large skeleton of Pentaceratops sternbergi (Ornithischia:Ceratopsia) provides for the first time an accurate impression of the body proportions in this horned dinosaur. This is the only known specimen with a skull associated with most of the postcranial skeleton. The restored skull is nearly three meters in length and is thus the largest of any ceratopsian and the largest skull thus far known in any terrestrial vertebrate. The elongate rostrum, elaborate premaxillary structure, and complex frontal and cornual sinuses demonstrate a high level of intraspecific variability in these features. Such features are therefore likely not useful in providing species-level discrimination in other chasmosaurines. The function of the intricate chasmosaurine premaxillary narial structures is probably associated with an advanced level of herbivory.

Middle Pennsylvanian, Atokan and Desmoinesian, crinoids and echinoids are described from the Belden and Minturn Formations of the Central Colorado Trough. The echinoderms from the Minturn Formation were living in an active intermontane trough setting. They are found in two environments, on the flanks of phylloid algal reefs and in patches on abandoned delta lobes on the gently sloping substrate. Faunas are dominated by cromyocrinids and are similar to stable platform Terrigineous Facies Belt faunas of the Midcontinent.

New species described are Dicromyocrinus beldenensis, Neoprotencrinus rockensis, and Sciadiocrinus wipsorum. Goleocrinus, and the columnal genera Blothronagma, Cyclocaudex, and Platyplateium are reported for the first time from the Minturn Formation. The columnal taxa Blothronagma cinctutum and Floricyclus angustimargo are believed to be cromyocrinids. B. cinctutum may be synonomous with Synarmocrinus molasensis, and Floricyclus angustimargo may be synonymous with Ulocrinus rockymontanus.

Two new cirroidean gastropod genera, Alaskiella (family Porcelliidae) and Alaskacirrus (family Cirridae), from the Emsian (late Early Devonian) of west-central Alaska (Medfra B-4 quadrangle) are described. The shell of Alaskiella medfraensis new genus and species exhibits inclined heterostrophic coiling. This shell character is known among other members of the subclass Archaeogastropoda, but is recorded for the first time within members of the superfamily Cirroidea. Inclined heterostrophic coiling of the shell was probably developed independently in several different groups of the subclass Archaeogastropoda. The new genus Alaskacirrus, represented by Alaskacirrus bandeli new species, is the oldest and only known Paleozoic member of the family Cirridae. This suggests that the family Cirridae was separated from the family Porcelliidae since at least Early Devonian time and that it most probably developed from the subfamily Agnesiinae of the family Porcelliidae. Thus, the stratigraphic range of the family Cirridae is at least from Lower Devonian to Cretaceous, an interval of about 350 million years.

A third known specimen of the ammonite Rhaeboceras burkholderi Cobban, 1987, has been discovered in the upper part of the Pierre Shale of early Maastrichtian age (Late Cretaceous) Baculites eliasi zone of Dawson County, Montana. This finding extends both the geographical and stratigraphic ranges of the species. In addition, R. cedarense new species is described from the Baculites baculus/grandis zone of the same region, which extends the stratigraphic range of the genus as currently recognized. The new species is a small form of Rhaeboceras that appears to be closely related to and probably descended from R. burkholderi.

Phacopida from upper Whiterock (Lower Caradoc) horizons in the Las Aguaditas Formation of San Juan Province, Argentina, include the calymenid Platycalymene trapezoidalis (Baldis and Pöthe, 1995) and the encrinurids Frencrinuroides edseli new species, Lasaguaditas oweni new genus and species, and Walencrinuroides? new species A. Sulcocalymene Baldis and Pöthe, 1995, a purported subgenus of Flexicalymene, is a junior subjective synonym of Platycalymene Shirley, 1936. Platycalymene is now known from Avalonia, Baltica, Laurentia (Scotland), and the Precordillera. Emending the cladistic analysis of Ordovician Encrinurinae by Lespérance and Desbiens (1995), the monophyly and membership of Frencrinuroides and Walencrinuroides are ambiguous. Frencrinuroides edseli is closely related to species from eastern Laurentia. Lasaguaditas new genus is superficially cybelinid-like in some respects but shares several derived characters with the Encrinurinae. All three encrinurinid species in the Las Aguaditas Formation possess two instars in the protaspid period, a general pattern in Ordovician encrinurinid ontogeny.

The following new Toernquistiidae from Whiterockian (Llanvirn to lower Caradoc) strata of the Precordillera, western Argentina, are described: Chomatopyge canasi new species, Lasarchopyge benedettoi new genus and species, Lasarchopyge correae new genus and species, Lasarchopyge new species A, and Paratoernquistia sanchezae new genus and species. Phylogenetic analysis suggests that the Toernquistiidae Hupé, 1953 (including Chomatopyge, Lasarchopyge, Mesotaphraspis, Paratoernquistia, and Toernquistia) is closely related to but distinct from the Dimeropygidae Hupé, 1953 (including Ischyrotoma, Ischyrophyma and Dimeropyge). It is difficult to find unique synapomorphies that unite toernquistiids and dimeropygids into a monophyletic group that excludes other proetides (e.g., hystricurids), although details of their ontogenies are similar. Several species of Toernquistiidae are known from the Argentine Precordillera (one species previously described), and other species of this family have been described from Australia, Baltica, China, Kazakhstan and Laurentia. Members of the Dimeropygidae are known only from Baltica and Laurentia.

On the basis of morphological and taphonomic study of a large sample population, Miaohephyton bifurcatum Steiner, emend. from the terminal Proterozoic Doushantuo Formation (600-550 Ma), South China, is interpreted as algal fragments shed from their parent thalli for reproductive or environmental reasons. Characters such as regularly dichotomous, multicellular thalli with forked tips, apical and intercalary meristematic growth, abscission structures, and possible conceptacles collectively suggest an affinity with the brown algae, in particular the order Fucales. In conjunction with reports of xanthophyte fossils in older Neoproterozoic rocks, this reinterpretation of Miaohephyton bifurcatum indicates that photosynthetic stramenopiles (chrysophytes, synurophytes, xanthophytes, phaeophytes, and diatoms; or chromophytes sensu stricto) diversified during the Neoproterozoic Era along with the red and green algae. This, in turn, suggests that the secondary endosymbiosis that gave rise to the photosynthetic stramenopiles took place relatively soon after the evolutionary transformation of cyanobacteria to rhodophyte plastids.

Based on material of the Upper Cambrian of Sweden the internal structure of proto-, para- and euconodonts has been investigated. The protoconodontids Gapparodus and Gumella show some special development of the median unit of the skeletal tissue. In Gapparodus, long, parallel-running lamellae suggest a continuous growth, even of previously secreted lamellae, until their eventual outcropping. In Gumella the fibrous median layer decreases considerably during growth until its complete reduction, which coincides with the disappearance of the posterior wall. Paraconodonts also produced several specialities in their mode of growth. Elements with lateral processes such as Proacodus and Serratocambria developed by allometric growth. The lamellae are much more widely spaced in the process than in the main cusp to attain the required length of the former. In Serratocambria additional lamellae are inserted in the process. Thin sections of tricuspidate westergaardodinids reveal paraconodontid growth with lamellar remains in the tip of the median denticle, which are isolated from the growth lines in the lateral denticles. Based on this observation a hypothetical growth model explains the lamellar development as a result of stress and strain. The Ordovician euconodontid Chosonodina clearly shows white matter and is thus unrelated, but homeomorphic to Westergaardodina. Cambropustula from the lower Upper Cambrian is the oldest euconodont yet but it lacks white matter. The latter was an evolutionary novelty, which progressively developed in the euconodont line.

The systematic position of conodonts is briefly discussed; the studied material cannot contribute to the hypothesis of neural crest derived skeletal tissue.