Phylogenetic reconstructions of two tropical American venerid genera, Chione and Chionopsis (subfamily Chioninae) were attempted at the species-level. The purposes of the analyses were to provide historical reconstructions of origination and extinction events in the two clades, as well as patterns of invasion and diversification. The analyses were based entirely on conchological characters to facilitate the inclusion of a substantial number of fossil taxa, but difficulties were encountered due to the quality of preservation and availability of material. Nevertheless the two genera were established as monophyletic clades, and the reconstructions yielded considerable insight into their histories in tropical America. The analyses suggest that both genera originated in the tropical western Atlantic, Chionopsis by at least the early Oligocene, and Chione in the early Miocene. Various branches of both genera subsequently invaded the tropical eastern Pacific several times prior to Seaway closure, with only one possible reciprocal invasion of the western Atlantic. Pliocene extinction affected both genera more significantly in the western Atlantic relative to the eastern Pacific, and diversity is higher today in the latter region. These conclusions are not entirely consistent with the fossil records of the genera, but this incongruency highlights the need for much more extensive sampling of the eastern Pacific Cenozoic record.

Previous descriptions of Tucetona lack a consistent system using diagnostic characters and only two recent Caribbean ‘species' are recognized. In this study, textural and structural features of the Tucetona shell are examined and used as the basis for comparison to other glycymerids and in the recognition of morphospecies. Standard diagnostic characters based mainly on the cross-sectional shape of ribs and on hinge teeth ontogeny are presented and used to distinguish six recent Caribbean morphospecies. The shell texture has been examined by light and scanning electron microscopy, showing the interior of glycymerid hinge teeth structured by two bundles of crossed lamellar texture. Whereas European Glycymeris examined for comparison correspond in their hinge plate textures to the one found in Tucetona, differences from a Caribbean Glycymeris sp. are described. Simple lamellar, crossed-lamellar and cone complex crossed-lamellar textures showed the same basic crystallite subunits.

Decapod crustacean specimens from the middle Eocene San Juan Formation in central Chiapas represent the first record of Eocene decapods in southern México. New taxa include: Dardanus mexicanus new species (Diogenidae), Lophoranina cristaspina new species, Notopus minutus new species (Raninidae); Verrucoides stenohedra new genus and new species (Xanthidae); Stoaplax nandachare new genus and new species (Goneplacidae); and Viapinnixa alvarezi new species (Pinnotheridae). Verrucoides verrucoides new genus and new combination from the Paleocene of Greenland represents a new combination. In addition, the fauna includes Callianassa sensu lato sp., Laeviranina sp., Calappilia cf. C. hondoensis Rathbun, 1930, Eriosachila sp., and indeterminate calappid and xanthoid taxa. This assemblage bears close relationship with coeval faunas in the Tethyan region of southern Europe and southern North America and with Paleocene faunas of Greenland, strengthening the evidence for previously described patterns of dispersal within the Decapoda.

Lower Ordovician sections in the type Ibexian area of western Utah contain a considerably more diverse trilobite fauna than has previously been reported. Reinvestigation of these faunas, based on new field sampling, allows a reassessment of the dimeropygid genera Ischyrotoma Raymond, 1925, and Dimeropygiella Ross, 1951. These taxa have been considered synonyms, but parsimony analysis indicates each is a well supported clade, and they are best recognized as sister genera. The number of species known from Ibex has been doubled, from four to eight, and morphological information is now available for most parts of the exoskeleton. New species include Ischyrotoma juabensis (Juab Formation), I. wahwahensis (Wah Wah Formation), Dimeropygiella fillmorensis (Fillmore Formation), and D. mccormicki (Fillmore Formation). The previously named species Dimeropygiella caudanodosa, D. blanda, and D. ovata are fully revised on the basis of abundant new material. Pseudohystricurus is a paraphyletic group, with species distributed as a basal grade of the Ischyrotoma/Dimeropygiella group.

Silicified kirkbyoid ostracodes from the Cantabrian Mountains (Spain) bear a striking resemblance to those of the Carnic Alps (Austria and Italy). The Spanish ostracodes come from the upper part of the Cuera Limestones (Bashkirian-upper Moscovian), which are exposed along the Playa de la Huelga section (Ponga Nappe) in the coastal area of eastern Asturias, northern Spain. These fossils were collected from upper Moscovian limestones deposited in an outer-platform environment. Most of the material from the Carnic Alps was obtained from the Nassfeld Pass area (eastern Carnic Alps), near the Austrian-Italian border, in limestones of the Kasimovian-Gzhelian Auernig Group and the Lower Permian Rattendorf Group. The several Auernig Group limestones that contain silicified ostracodes were deposited in a shallow-marine environment.

Despite the differences in age (according to fusulinids and conodonts), these kirkbyoids are very similar and in some cases identical. Coronakirkbya pramolla new species and Kirkbya carniacantabrica new species occur in both areas. Two other pairs of species, Coronakirkbya krejcigrafi Becker, 1978, and Coronakirkbya carina new species, and Aurikirkbya cf. beckeri (Kozur, 1990) and Aurikirkbya carinthica new species, show close affinities, though they are considered to be different species. Most of the species described herein are either very rare or absent in other regions.

The close paleobiogeographic relationships between the Cantabrian Mountains and the Carnic Alps, documented previously only by brachiopods, are confirmed.

A new, flattened, eocrinoid-grade, blastozoan echinoderm Haimacystis rozhnovi new genus and species is described from the uppermost Lower Ordovician Wah Wah Limestone of western Utah. Although apparently most similar in morphology to the rhipidocystids, Haimacystis differs in its plane of thecal flattening, lack of one-piece marginals, and ambulacral system development. A comparison of overall morphology and plane of thecal flattening is presented for flattened blastozoans. Haimacystis was a streamlined suspension feeder attached to the sea floor by a holdfast at the end of a relatively short stem and bent over in the water column in moderate currents.

Silurian ramphoprionid polychaete annelids, represented by their jaws (scolecodonts), are described from extensive collections from Gotland, Sweden. The family Ramphoprionidae, monotypic at its original description, is sub-divided into four genera; Protarabellites Stauffer, 1933; Ramphoprion Kielan-Jaworowska, 1962; “Pararamphoprion” Männil and Zaslavskaya, 1985; and Megaramphoprion new genus. Identified species include “P.” cf. nordicus Männil and Zaslavskaya, 1985; P. rectangularis new species; P. staufferi new species; P. triangularis new species; and two Protarabellites species left in open nomenclature. Ramphoprion is represented by one new highly plastic species, R. gotlandensis, housing five distinguishable morphotypes showing gradual evolution. Megaramphoprion, which is most closely related to Ramphoprion, is represented by M. magnus new genus and species, a rare but distinctive taxon. Most species have long stratigraphic ranges within which important morphological changes can nonetheless be observed. The stratigraphic range of ramphoprionids includes, at least, the Ordovician to the Silurian. They are fairly rare in the Silurian of Gotland and where present they generally form less than 10 percent of the polychaete faunas, although occasionally reaching as much as 20 to 30 percent. Evolution, paleoecology, and surface structures of the investigated species are briefly discussed.

Exceptionally well-preserved Late Mississippian colosteid amphibian specimens occur in southern Illinois; the mandible is described here. Unexpectedly primitive features include toothed adsymphysial and intercoronoid fossa with fenestrate floor. The large adsymphysial bears teeth, forms 50 percent of the symphysis, and meets its antimere in a very coarsely rugose suture. These and other characters are shown to occur also in Greererpeton burkemorani, to which we refer the Illinois specimens. Colosteid mandibles from a Late Mississippian locality in southern Iowa resemble G. burkemorani closely, although they are not conspecific. Our findings are summarized in a PRESERVE-format data table containing 226 characters. G. burkemorani's adsymphysial suture morphology is shared with the baphetid Megalocephalus pachycephalus. However, the relationship of colosteids to other Paleozoic amphibian groups remains unclear, beyond their position as stem tetrapods. The single elongate Meckelian fenestra of colosteids is likely primitive for tetrapods. A three-stage model is proposed for the evolution of Meckelian fenestrae in tetrapods. Based on sutural morphology, G. burkemorani is considered to have a kinetic joint between skull table and cheek. A functional hypothesis is outlined in which movements at this joint are accommodated at the symphysis. A phylogenetically based test of this hypothesis is proposed.

Leptarctus is a poorly known fossil carnivore that ranges through the Miocene of North America and Inner Mongolia, China (Lim, 1996; Zhai, 1964). Though it has been one of the least studied carnivores, more than 20 localities in North America have produced Leptarctus (Lim, 1999). The characters diagnosing Leptarctus as a mustelid include absence of M2, absence of a notch between the blades of the upper carnassial, and a reduced dentition with loss of PI and pi. Though Leptarctus is a mustelid, the teeth bear many similarities to those of procyonids, Procyon lotor and Nasua nasua and stand as a remarkable example of dental convergence (Leidy, 1856; Lim, 1999). Unlike other mustelids, Leptarctus has prominent double sagittal crests, heavy zygomatic arches, a prominent occipital crest, a well-developed hypocone on P4, labially curved upper canines, grooved lower canines, raccoon-like mandibles, elongated metatarsals, and unique bony projections on the tympanic bullae (Lim, 1999).

Large rostroconchs have been described from Europe by Sowerby (1815), M'Coy (1844), Baily (1871), Halfar (1882), de Koninck (1885), Hind (1900), and Amler (1996). This report concerns the first known occurrences of rostroconchs from Iran (Fig. 1). The specimens are from the Devonian Bahram Formation (Famennian) (Dastanpour, 1996; Dastanpour and Bassett, 1998; Brice, 1999; Brice et al., 1999) and the Mississippian Mobarak Formation (Tournaisian-Vis6an) (Gaetani, 1968; Bozorgnia, 1973). The Devonian specimens were collected from limestone and argillaceous limestone associated with a diverse brachiopod fauna (Fig. 2). The Mississippian specimens were found in limestone with brachiopods, corals, and crinoids (Fig. 3).