...K. O. Emery Abstract The commonest and most stable position of empty valves of large pelecypods on the wave-washed zone of beaches is concave down; this position is due to the presence of fast currents and the absence or inadequacy of bioturbation. In contrast, most large pelecypod valves...

...H. Edward Clifton Abstract Participation in man-in-the-sea experiments Tektite I and II permitted an examination of the orientation of pelecypod shells and shell fragments on sediment unaffected by waves or currents. Whether on vegetated or unvegetated unrippled sand or on solid coral...

...Guy Mennessier Abstract Rudistid pelecypods belonging to the genus Plagioptychus from Cretaceous localities of Europe are revised, Two groups, one Turonian and the other Senonian, are differentiated by the position of the P IV tooth. The evolution of both groups is characterized by complication...

... in concentration values were found for different pelecypod genera and on different shell surfaces of the same genus. There is positive correlation between uranium concentration of the internal and external valve surfaces and concentrations of uranium in the associated water environments. Ocean waters contain about...

...Guoxiang Li; Zhifei Zhang; Hong Hua; Huining Yang A bstract The early Cambrian calcareous skeletal fossil Apistoconcha Conway Morris is characterized by its two valves having posterior teeth and internal umbonal cavities. It has been reported from lower Cambrian Botomian-equivalent carbonate rocks...

... on ammon- oids and pelecypods . Each section bears a table showing the stratigraphic position o f selected rock units and a summary of fossil ranges (Tables 1-8) . These rock-unit correlations should be considered only as a guide . Lack of space prevents the inclusion of all known units, and it goes...

... consist of parallel laminae, often slightly inclined, with minor discordances, erosive bases and weak grading. A striking aspect in these skeletal layers is the presence of well-preserved articulated, double-valved ostracods or pelecypods (pl. I, figs 2 and 6 ). This strongly suggests rapid winnowing...

... dentition taxodonte sont examinés et évalués en annexe. [Traduit par la Rédaction] Palaeotaxodonts having taxodont dentition are among the most widespread and diverse groups of Ordovician pelecypods. Large faunas of Ordovician pelecypods have been described from Australia, Europe, North America...

..., 1972 ; Amler, 1989 ). The single specimen of Parallelodon ? from the Mucambo dolostone (bed 1) is preserved as an external mold of articulated valves. Meekopinna ? americana from the Esperança dolostone (bed 4) occurs commonly in life position with articulated valves perpendicular to bedding...

...JOSEPH G. CARTER The specimens of Pteronites americana were found with their shell valves closed and their broad sides parallel to bedding planes. Postmortem compaction apparently produced a reflection of their ligament grooves and ridges on the exterior of the regular simple prismatic outer...

... brachiopods, thicker and flatter valves are preserved preferentially, while thinner and more convex valves preferentially are destroyed. Roy et al. (1994) showed that, for pelecypods in point-load compression, unbored shells are more resistant to fracture than bored shells. Laboratory biomechanical work...

...- in Platystrophia ponderosa result from preferential destruction stones. of the thinner brachial valve, rather than from selective trans- The Mount Auburn Member has been interpreted as an portation of one valve, as observed for pelecypods. Differences in offshore shoal, deposited above fair-weather wave base...

... with valves in butterfly position, paratype, MLP 6265a (same specimen illustrated by Leanza, 1942 , pl. 19, fig. 3 as ‘Gen. et sp. indet.’); ( 13, 14 ) left valve, paratype, MLP 35773, in dorsal ( 13 ) and lateral ( 14 ) views; ( 15 ) specimen with both valves slightly displaced, paratype, MLP 35792...

... to very fine-grained sandstone bed, three peculiar specimens were collected by the late R. Brunet, who generously allowed us to describe them. The unique material includes a left and a right valve of two different specimens, and an internal mold of a closed shell. The internal mold is unfortunately...

... parallel to the commissure showing series of teeth size and position of the resilifer (r), right valve, specimen PIMUZ 28455. 1, section through the resilifer, showing ventral extension of this structure; 2–4, sections with decreasing distance to plane of commissure, showing disappearance of resilifer...

... remember the ease with which a brachiopod can be mis- taken for a pelecypod. In the former the beak is central with mirror image on either side. In pelecypods the beak is usually off-centre, giving an assymet- rical appearance to the shell. In profile the valves of brachiopods arc generally of differing...

... lucifuga n sp. holotype SGO.PI.23102. ( 1, 7 ) General view of the valves in butterfly position; ( 2 ) view of posterior area showing thickening of shell giving way to the chondrophore (cr) where the internal ligament is situated; white arrow indicating position of detail; ( 3 ) enlarged detail...

... penetrations perpendicular to the valve surface. Incomplete, healed, and multiple holes are absent. Drilling frequency, a proxy for predation intensity, is very low: less than 1 percent (this estimate may be seriously affected by taphonomic and monographic biases). Literature data suggest that frequency...

... in front of mid-length; ends rounded, posterior end typically produced at its ventral bend, and in some instances extended or caudate at this position; dorsal slopes subtruncate. Left valve slightly larger than right; in some species right valve overlaps along ventrum. Surface smooth or finely papillate...

... Devonian is based -upon it s stra.tigraphie position between the Givetian Bird Fiord (Mel wren, 1963, p . 615) and Frasnian to Famennian Griper Bay Formations . A reference section of the Griper Bay Formation is here established fo r easterly-dipping exposures near the mouth of an easterly-flowing stream...