Silurian and Devonian bivalves recovered from the Los Espejos (Silurian to Lower Devonian) and Talacasto (Devonian) Formations of the Northern Precordillera Mountain belt are described and illustrated. The fauna comprises some new nuculoids Deceptrix (Devonodeceptrix) jachalensis n. subgen. and n. sp., Nuculites argentinum n. sp., and Anthracoleda (Pseudoleda) minuta n. subgen. and n. sp., as well as the new pterioid Actinopteria modesta n. sp. Additionally, many poorly known South American bivalves are redescribed and figured. Silurian–Devonian pelecypod faunas from some South American localities show differences both in diversity and in faunal composition. Causes for these differences are briefly discussed. Controls other than latitude are suggested in order to explain biogeographical affinities of the studied fauna.

The new subfamily Struthiopterinae is proposed for the aporrhaid gastropods occurring in the Late Cretaceous-early Tertiary Weddellian Province along the southern margin of the Pacific. The following genera are placed within the Struthiopterinae: Struthioptera Finlay and Marwick, 1937; Austroaporrhais n. gen.; and Struthiochenopus n. gen. The temporal and biogeographic distribution of members of Struthiopterinae show a similar pattern to other Southern Hemisphere groups of Late Cretaceous and early Cenozoic molluscs with initial disappearance from the western Australasia of the Weddellian Province by the Paleocene while surviving in Antarctica until the late Eocene and eventually disappearing in southern South America during the early Miocene.

Also included in this paper is a reappraisal of the species assignable to these genera from Late Cretaceous and early Tertiary of New Zealand, Antarctica, and southern South America together with the description of five new species. The following new species of the Struthiopterinae are described: Austroaporrhais larseni n. sp., A. stilwelli n. sp., A. dorotensis n. sp., Struthiochenopus antarcticus n. sp., and S. philippii n. sp.

The presence of Swiftopecten Hertlein, 1936, in Patagonia (Argentina), a region situated in the southeastern extreme of the South American continent, is the oldest and southernmost fossil record of the genus. Furthermore, its occurrence during the Late Eocene in the circum-Antarctic region suggests that its origin was in the Southern Hemisphere; it has been known from Japan and the eastern Pacific, ranging from Miocene to Holocene (Moore, 1984). Swiftopecten iheringii new species, from the Late Eocene-Early Miocene sedimentary sequence of Patagonia, is described and illustrated.

The discovery of domatial dimorphism in the leperditellid ostracode Loculocavata n. gen. and the monotiopleurid Primitiella minima (Harris), and the possibility that Leperditella Ulrich exhibits domatial dimorphism, requires a revision of the concept and/or diagnosis of the Platycopina. Domatial dimorphism is manifested by a special domiciliar space for egg/brood care in females. Domatia are represented by a loculate domiciliar wall or by a more generalized space bounded anteriorly by an interior partition caused by thickening or folding (sulcation) of the shell wall. Domatial dimorphism occurs in morphologically diverse ostracodes as shown by the podocopine Mesocyprideis, kloedenellids, cytherellids, monotiopleurids, the leperditellid Loculocavata n. gen., and by its possible occurrence in Hypotetragona and Leperditella. Changes in the present concept and/or diagnosis of the Platycopina are required to account for the above. Possible classifications range from restricting the Platycopina to holosolenic ostracodes with R/L overlap and domatial dimorphism to including within the Platycopina all groups that exhibit domatial dimorphism. The position of adductor muscle attachment in Loculocavata n. gen. and Primitiella minima (Harris) suggests that L2 may be the external expression of the position of adductor muscle attachment in some ostracodes.

Iberonepa romerali n. gen. and sp. is the most abundant insect species found in Lower Cretaceous (Barremian) lithographic limestones at “Las Hoyas,” Spain. External features of this species indicate that it should be assigned to the family Belostomatidae, with a similarity to the species Stygeonepa foersteri Popov, 1971, which was found in the Upper Jurassic (Tithonian) lithographic limestones of Solnhofen. This article discusses the relation between these two species and subfamilies of the Recent Belostomatidae. The new “Las Hoyas” species is described from adult specimens and from molts of nymphs, these differing only slightly from one another. The abundant number of specimens and the generally exceptional preservation have allowed interpretation of its probable natatory behavior on the basis of the functional morphology of the insect's legs.

Stirpulina saulae n. sp. is the first reported clavagellid from the Pacific Province of North America. Specimens of this clavagellid are from the Ladd Formation of the Santa Ana Mountains, Orange County, southern California. The age of these specimens is Late Turonian based upon the presence of the ammonite Subprionocyclus spp. both above and below the clavagellids in the section. These are, therefore, the oldest reported clavagellids from the western hemisphere, and they give positive support to the European Turonian reports of the genus Stirpulina. The deposits indicate an open-shelf habitat of shallow to moderate depth, and the associated fauna suggests a warm temperate to subtropical marine climate. This is consistent with the previously reported Cretaceous distribution for the group.

Molluscan assemblages from upper middle Eocene deposits of southwestern Washington represent a regional biotic system that provides independent evidence of a range of depositional environments in a delta. Four marine molluscan assemblages reflect a subtropical fauna that inhabited an inner neritic to upper bathyal gradient down the prodelta slope. Comparisons with Recent molluscan taxa indicate changing trophic structures from dominantly infaunal filter feeding in the shallow, coarser-grained substrate to dominantly infaunal deposit feeding in the fine-grained mud. A very high diversity of carnivorous gastropods indicates that the biocenosis included a wide array of predominantly errant, soft-bodied invertebrate prey. The most shallow marine assemblages show evidence of dense Turritella patches within infaunal bivalve-dominated associations, indicating mosaics of distribution across a soft-sediment substrate. Low diversity marginal-marine and freshwater assemblages show faunal links with each other. They indicate interdistributary bay and marsh environments that are commonly part of a river-dominated delta.

The stratigraphic section at Aidaralash Creek, northern Kazakhstan, provides a complete and well-developed succession of strata across the Carboniferous–Permian boundary. This section, containing abundant and well-preserved ammonoid, fusulinacean, and conodont faunas, can serve well as the Carboniferous–Permian boundary stratotype. A profound change in ammonoid faunas, which occurs at the Orenburgian–Asselian boundary and which has been recognized by previous workers (e.g., Ruzhencev, 1950, 1951, 1952; Bogoslovskaya and Popov, 1986a, 1986b; Furnish, 1973; Glenister and Furnish, 1981), occurs in the Aidaralash Creek section, at the boundary between beds 19 and 20, and serves to mark the Carboniferous–Permian boundary. Additionally, Lower Permian strata at Aidaralash Creek mark the first appearance of widespread Permian ammonoid taxa, including representatives of Svetlanoceras, Juresanites, Prostacheoceras, Tabantalites, and Kargalites, that are preceded by the extinction of characteristic Late Carboniferous genera such as Prouddenites, Uddenites, Shumardites, Vidrioceras, Schistoceras, and Subkargalites.

A well-preserved mouth apparatus consisting of jaws and a radula was found in situ within the body chamber of the goniatite Cravenoceras fayettevillae Gordon, 1965 (Neoglyphiocerataceae: Cravenoceratidae), from the middle Chesterian (Upper Mississippian) of Arkansas. Both upper and lower jaws consist of a black material. The lower jaw is characterized by a widely opened larger outer lamella and a shorter inner lamella. The upper jaw is fragmental. The radula is preserved in the anterior portion of the buccal space and comprises a series of tooth elements. Each transverse tooth row consists of seven teeth (a rhachidian and pairs of two lateral and one marginal teeth), with a pair of marginal plates. This arrangement is typical of radulae of other ammonoids of Carboniferous to Cretaceous age, coleoids, and the orthoconic “nautiloid” Michelinoceras (Silurian, Michelinocerida), suggesting a phylogenetic affinity among them.

Agnostus acadicus Hartt (in Dawson, 1868) was the first agnostoid trilobite to be described from Middle Cambrian strata in North America. It was later designated the type species of Acadagnostus Kobayashi, 1939. The original description of A. acadicus was based on two specimens, a cephalon and a pygidium, which are illustrated for the first time with photographs. These are interpreted to represent separate species, each belonging to a different genus. The holotype cephalon is reassigned as Peronopsis acadica, which is judged to be a subjective senior synonym of Agnostus fallax Linnarsson, 1869, and several other species-group taxa. Consequently, Acadagnostus is suppressed as a subjective junior synonym of Peronopsis. Agnostus fallax is the type species of Axagnostus Laurie, 1990, which also is suppressed as a subjective junior synonym of Peronopsis. The pygidium on which the original description of A. acadicus was based is reassigned to Hypagnostus parvifrons (Linnarsson, 1869).

Peronopsis acadica, as emended, is a common, cosmopolitan agnostoid in open-marine lithofacies. It has an observed stratigraphic range from the Ptychagnostus praecurrens Interval-zone to the Ptychagnostus punctuosus Interval-zone.

A well-preserved and diverse ostracod fauna of late Eocene, Kaiatan Stage age is described from a mudstone sample (Ashley Mudstone Formation) from the Waihao River outcrop near McCulloch's Bridge, South Canterbury, New Zealand. A total of 8,662 specimens are assigned to 104 species including one new genus and 13 new species. Of the new species all but the Cytheruridae are described herein. The new genus is Taracythere, type species T. proterva (Hornibrook, 1953) and the new species described here are: Pseudeucythere biplana, Eucythere sulcocostatula, Copytus pseudoelongatus, Neocytherideis reticulata, Patagonacythere waihaoensis, Munseyella pseudobrevis, Actinocythereis microagrenon and Pennyella leptodictyota. Because of a need for reillustration of established species, most of the remaining 91 species are illustrated and the systematics of some of these is remarked upon. Sixty-two species have been previously described, eight are tentatively referred to previously described species, and 21 are left in open nomenclature mainly due to paucity of material. The assemblage is interpreted as having lived in a low energy marine environment on the outer shelf or upper slope. Comparison with contempory ostracod faunas of southeastern Australia indicates very high affinity: 56 common genera, out of the 61 genera listed here. Considering the timing of Tasman seafloor spreading (Paleocene to Middle Eocene) and foundering of continental crustal regions of the eastern Tasman Basin to bathyal depths (initially Middle Eocene), trans-Tasman ostracod dispersal probably predates late Eocene times. The greater number of endemic Eocene genera recorded in Australia suggests that migration was dominantly eastwards.

The cassiduloid echinoid Calilampas californiensis n. gen. and sp. is described from middle lower Eocene (“Capay Stage”) shallow-marine sandstones in both the middle part of the Bateque Formation, Baja California Sur, Mexico, and the lower part of the Llajas Formation, southern California. The new genus is tentatively placed in family Pliolampadidae. The cassiduloid Cassidulus ellipticus Kew, 1920, previously known only from the “Capay Stage” in California, is also present in “Capay Stage” shallow-marine sandstones of the Bateque Formation.

Previous studies of the Toarcian of the North American Cordillera have mentioned the rare occurrence of Paroniceras in the Queen Charlotte Islands. Recent work has identified the presence of Leukadiella in the Middle Toarcian of the Queen Charlotte Islands, the Spatsizi area, and the Hazelton area. They occur with Rarenodia planulata, Peronoceras pacificum, Peronoceras verticosum, and Phymatoceras cf. P. pseudoerbaense. The Leukadiella specimens are well preserved and generally larger than those found in the Mediterranean region. Taxa present in North America include Paroniceras sternale, Leukadiella ionica, Leukadiella amuratica, Leukadiella aff. L. helenae, and Leukadiella aff. L. ionica. Morphologically Leukadiella is closely related to such genera as Hildaites and Hildoceras and is more suitably placed within the subfamily Hildoceratinae rather than the Bouleiceratinae. The distribution of Leukadiella and Paroniceras indicates the influence of the Hispanic Corridor linking western Tethys and the eastern Pacific during the Middle Toarcian.

Walcott described the If fauna from Silver Peak Range, Nevada in 1910 as consisting of Nevadia weeksi n. sp. and gen. and Holmia rowei n. sp. (herein recognized as Esmeraldina rowei). Being the oldest trilobite fauna known at the time, it played an important roll in Walcott's locating the base of his Lower Cambrian Waucoban Series. The original If collection is reviewed, as is more material collected near the type locality, “Nevadella” Zone, Montenegro Member of the Campeto Formation. Additional trilobite taxa herein recognized in the If collection are Esmeraldina? cometes n. sp., Esmeraldina lidensis n. sp., Palmettaspis consorta n. gen. and sp., and Palmettaspis parallela n. sp. A close similarity between E. rowei and the type species for Holmia in Baltica led Walcott to a controversial Laurentia–Baltica correlation. His incorporation of three trilobite taxa among his syntypes for Holmia rowei also posed a problem. Overriding these faults was Walcott's foresight in using the 1f fauna in his Waucoban concept. Even today, after the 1992 international agreement to lower the base of the Cambrian to a pre-trilobite horizon, the Waucoban is being applied in Canada to upper Lower Cambrian strata.

The Early Permian (late Sakmarian to early Artinskian) adrianitid ammonoid Nevadoceras steelei new genus and species occurs in a fauna containing the ammonoids Properrinites Elias, Prothalassoceras Böse, Daraelites Gemmellaro, Almites Toumanskaya, Bamyaniceras Termier and Termier, Akmilleria Ruzhencev, Agathiceras Gemmellaro, Metalegoceras Schindewolf, Stenolobulites Mikesh, Glenister, and Furnish, Crimites Toumanskaya, Neocrimites Ruzhencev and the conodonts Sweetognathus whitei (Rhodes) and Mesogondolella bisselli (Clark and Behnken). This fauna occurs in a concretionary interval within micritic basinal facies of the Dry Mountain trough at Portuguese Springs, White Pine County, east-central Nevada.

Recurring associations of the trilobite ichnogenus Rusophycus with various “worm” burrows suggest an interaction between the two tracemakers, specifically, capture of the worm by the trilobite. An exceptional ichnofossil from the Upper Ordovician of southwestern Ohio shows characters consistent with previously described “trilobite hunting burrows” from Cambrian and Silurian strata. Preserved in convex hyporelief is R. carleyi, attributable to the trilobite Isotelus, on which is superimposed the case of a worm burrow of the ichnogenus Palaeophycus. The cast of the worm burrow appears to have been truncated by the digging activities of the trilobite, suggesting its predation of the worm. The exquisite preservation of ventral axial morphology of the trilobite distinguishes this Rusophycus from simpler bilobate forms attributable to filter-feeding behavior. Congruency in the preservation of worm and trilobite trace supports the conclusion that both were created at the same time, as the trilobite exited the intrastratal burrow. This is the first report of a trilobite hunting burrow from the Ordovician, and the first evidence for predatory behavior for the trilobite genus Isotelus.

Maurotarion Alberti, 1969, is a diverse otarionine clade that can be readily distinguished from Harpidella M'Coy, 1849. Both genera appear in the Upper Ordovician and range until the Middle Devonian. A new diagnosis for each taxon is given. New species of the genera from the Ordovician and Silurian of the central Mackenzie Mountains, Northwest Territories, Canada, include Harpidella kurrii (Ashgill), H. tikkaneni (Llandovery), H. greggi (Wenlock), and Maurotarion messieri (Llandovery). Harpidella megalops (M'Coy, 1846), H. triloba (Hu, 1975), H. spinafrons (Williams in Cooper and Williams, 1935), Maurotarion struszi (Chatterton, 1971), and M. instita (Whittington and Campbell, 1967) are revised.

The first Silurian trilobites to be described from Alaska are of late Llandovery (Telychian) age. They occur with original cuticle intact in a white biosparite. Seven species have been identified, including Paracybantyx occidentalis n. sp., Ligiscus smithi n. sp., Calymene s.l. aff. C. iladon Lane and Siveter, 1991, Scotoharpes aff. S. raaschi Norford, 1973, Scharyia sp., a cheirurine belonging to either Radiurus Ramsköld, 1983, or Protocerauroides Chatterton and Perry, 1984, and an undetermined warburgelline. The fauna has close affinity to those described from similar lithologies in the Telychian of North Greenland. Machaeridians occurring with the trilobites include Turrilepas sp., Compacoleus sp., and Lepidocoleus cf. L. britannicus Withers, 1926.

The genus Lobocarcinus Reuss, as it is currently understood, consists of five species. Three of these species are retained: L. paulinowurtembergensis, L. indicus, and L. aegypticus. Lobocarcinus catalaunicus is referred to Neptunus, and L.? santosi is referred to Cancer. A new species, L. lumacopius, is described. Lobocarcinus forms are distinct from all other cancrids in the lobation of their anterolateral margins, high width: length ratio, and dorsal carapace ornamentation. The type species of the genus, L. paulinowurtembergensis, is abundant in the Gebel Mokattam region near Cairo. The studied specimens of L. lumacopius are from Wadi Hitan (Zeuglodon Valley), a region approximately 140 km southwest of Gebel Mokattam in the Fayum Depression. Direct comparisons are made between L. lumacopius and L. paulinowurtembergensis, and sexually dimorphic characters of L. lumacopius, including width: length ratios and abdominal and sternal elements, are identified. A key is presented to aid in the identification of the various species within the genus and to help in distinguishing Lobocarcinus from Cancer.

The Orthograptus quadrimucronatus species group currently comprises 22 taxa, which, with the exception of O. ruedemanni, are distinguished from other orthograptids by the presence of paired apertural spines on their thecae. A detailed morphometric analysis of this group indicates that these taxa comprise four basic morphotypes that actually represent only six distinct species: O. pageanus, O. quadrimucronatus, O. spinigerus, O. ruedemanni, O. eucharis, and O. rivai.

Specimens of Orthograptus pageanus have a rapidly widening rhabdosome with elongated spines on the first two or four thecae. Orthograptus pageanus is divided into two chronological subspecies, an older, smaller form, O. pageanus pageanus, and a younger, larger form, O. pageanus maximus n. subsp. Specimens of O. spinigerus have elongated spines on one or two thecal pairs between the sixth and thirteenth thecal pairs, a very narrow proximal end, and a rapidly widening rhabdosome. Specimens of O. quadrimucronatus have a more parallel-sided shape and no unusually long spines. The subspecies O. quadrimucronatus richmondensis is differentiated by the absence of both a median septum and a th 12 spine. Orthograptus ruedemanni, O. rivai, and O. eucharis are all dwarf forms.

Within a chronostratigraphic framework based on K-bentonite bed correlations the pattern and process of evolutionary change in the members of the O. quadrimucronatus species group is examined. Morphometrically, each species remains a coherent entity through time, occupying its own distinct morphospace. Each speciation event probably occurred rapidly, precluding the preservation of intermediates, and the new species retained their basic morphology throughout their existence. Within these lineages, phyletic changes were either absent or encompassed only changes in size, even when accumulated for much longer intervals than would be expected for speciation events. These patterns appear to be consistent with the evolutionary model of punctuated equilibrium.