Tarphophragma

COMPARISON

DIAGNOSIS. — Ramose colonies with a few generations of encrusting autozooecia at the colony bases; branch cross section shape circular. Irregularly shaped, elevated maculae present and composed of cluster of macrozooecia and mesozooecia. Budding pattern interzooidal. Autozooecial arrangement disordered. Autozooecia characterized by ontogenetic progression mesozooecia expanding into autozooecia, bending gradually from the endozone through the exozone, having polygonal to subpolygonal to subcircular shape in the endozone. Autozooecial diaphragms closely spaced in early ontogeny and in late ontogeny in all species and occasionally throughout ontogeny in some species, intersecting walls at different angles, shaped usually planar, convex, concave or cystoidal, spaced variably. Autozooecial wall structure integrate in deep exozone, occasionally less integrate in shallow exozones of some species, having straight to irregular boundary in the exozone; wall laminae sharply convex distally, thickened greatly in exozone. Reduction in abundance of mesozooecia and change in autozooecial living chamber cross section shape in exozone from circular to subpolygonal; deeper sections show autozooecia with more circular living chamber cross sections, thinner walls, and almost completely isolated by mesozooecia; shallower sections show autozooecia with more subpolygonal living chambers cross sections, thicker walls, and mesozooecia less abundant. Mesozooecia common, but not isolating autozooecia; occasionally fusing to form autozooecia, having thinner walls than those in autozooecia. Acanthostyles, cystiphragms, mural spines or cup-like aparati (sensu Conti & Serpagli 1987) absent.

The genus Tarphophragma Karklins, 1984 differs from other halloporid genera by the integrate wall structure and the budding pattern of autozooecia which derive from mesozooecia in endozone.

OCCURRENCE. — Middle – Upper Ordovician; worldwide.

TYPE SPECIES. — Monotrypella multitabulata Ulrich, 1886 by subsequent designation (Karklins 1984). Decorah Shale and Prosser Limestone, Mohawkian, Upper Ordovician; Minnesota, United States.