Scenella

Abstract: Yochelson, Ellis L. & Stanley, George D., Jr. 1981 12 15: An early Ordovician patelliform gastropod, Palaelophacmaea, reinterpreted as a coelenterate. Lethaia, Vol. 15, pp. 323–330. Oslo. ISSN W24–1164. The fossil Palaelophacmaea criola Donaldson, from the early Ordovician Stonehenge Formation of central Pennsylvania, was described as a patelliform gastropod. A reinterpretation of the type lot and study of a few additional specimens provide the basis for an alternative placement. Palaelophacmaea is here assigned to the Hydrozoa, as a possible chondrophore. It has an exceptionally thin shell or test and concentric but irregular corrugations. Cambrian univalve genera having a more or less circular outline that are currently assigned to the Gastropoda or Monoplacophora should be reexamined to see whether they have the features of fossil chondrophore coelenterates rather than those of molluscs. The late Cambrian Palaeoacmaea Hall & Whitfield is removed from the monoplacophoran Mollusca and left unassigned as to phylum. We judge that at least some early Cambrian species of Scenella are probably coelenterate remains. *Early Ordovician, Palaelophacmaea, Gastropoda, Monoplacophora, Hydrozoa.

Abstract: An analysis of the fauna of the Lower Cambrian Monkton Quartzite indicates the presence of 5 brachiopods, of which 3 are identified specifically; 1 unnamed new gastropod; 2 species of Hyolithes; and 6 species of trilobites, of which 5 are identified. All identified species occur in the lower Parker Slate or upper Dunham Dolomite of the St. Albans region. The fossil evidence demonstrates that the Monkton and the Parker are lateral facies of a once-continuous unit and that their present geographic separation is due to later erosion. All species are described. No new taxa are noted from the Monkton fauna, but the gastropod genus Scenella is considered and a new subgenus Protoconchoides, is proposed, as well as the new species Scenella (Protoconchoides) palmeri from the Lower Cambrian Pioche Shale at Eureka, Nevada. The classification of the Lower Cambrian ptychopariid trilobites is reexamined and 2 families, Antagmidae Hupe and the Eoptychopariidae, n. fam., are recognized. The Antagmidae contain 3 subfamilies, 6 genera, 2 named subgenera, and 22 assigned Lower Cambrian species. None of these taxa is new. The Eoptychopariidae contain 3 new subfamilies, Eoptychopariinae, Hadrokraspedinae, and Austinvilliinae; 5 genera, of which Hadrokraspedon is new; 2 subgenera, of which Cyphambon is new; and 16 species, none of which is new. Two genera and 4 species are noted whose classification is not determined.

Abstract: The cap-shaped Scenella(?) discinoides Schmidt, 1888 is redescribed on the basis of the type material from the Lower Cambrian of Estonia and assigned to a new genus Estoniadiscus. Shell morphology, the apparent phosphatic composition and the presence of probably setigerous tubes perforating the shell indicate that Estoniadiscus is neither a mollusc related to Scenella Billings, 1872, nor a chondrophorine hydrozoan. Following comparison with several other problematic Cambrian metazoans it is concluded that Estoniadiscus may be a stem group brachiopod.