The Stromatoporoid Genera Tienodictyon, Intexodictyon, Hammatostroma and Plexodictyon

These four genera have regular, thin, compact, laminae and irregular interlaminar tissue in which the pillars intertwine to produce a tangled structure. Intexodictyon (Llandovery to Ludlow) has pillars some of which cross the interlaminar space on oblique or vertical courses and many which branch upward joining their neighbors to produce secondary laminae. The primary laminae are netlike. Plexodictyon (Ludlow) has secondary laminae folded in a chevron or zig-zag pattern between solid primary laminae. Hammatostroma (Lower Devonian-Frasnian) has a tangle of pillar fibers in the central area between solid laminae. Tienodictyon (?Middle Devonian) is characterized by a lower interlaminar zone where pillar tissue forms a network and an upper zone of columnar pillar structure. The holotypes of Tienodictyon zonatum and Clathrodictyon cystosum lineatum are redescribed and a new species of Plexodictyon, P. waparksi, is established. Plexodictyon is believed to have evolved from Ecclimadictyon or directly from Clathrodictyon stock. Intexodictyon seems to be related to both Clathrodictyon and Actinostroma and closely resembles Atelodictyon. Tienodictyon and Hammatostroma are Devonian branches from an Anostylostroma stock characterized by fibrous tissue.