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- C5 Sequence (Lower Whitewater)
Identification in Hand Sample:
- Unbranched, bifoliate, and proximally tapering zooarium
- Subrectangular zooecia arranged in multiple long straight rows
- Colonies grow from pointed proximal tips
- Mesopores and acanthopores are lacking
- Living chambers are elliptical to subrectangular in cross section
Ptilodictya magnifica from the Whitewater Formation of Cedar Creek, Ripley County, Indiana (MUGM 22043)
Steve Holland (2013, UGA Strat Lab):
- Unbranched, bifoliate, and proximally tapering zooarium (lanceolate), with subrectangular zooecia arranged in multiple long straight rows
Treatise on Invertebrate Paleontology (1983):
- Zoarium lanceolate with tapering proximal segment. Mesothecae straight, rarely zigzag locally. In endozones, autozooecia in straight ranges, subrectangular to subhexagonal in cross section. In exozones, autozooecia in straight ranges, arranged in rhombic to reticulate pattern in adjacent ranges; contiguous; commonly subrectangular in cross section, few irregularly polygonal in lateral regions. Autozooecial boundaries generally not visible; pustules rare. Living chambers elliptical to subrectangular in cross section; lining common in endozones, discontinuous or lacking in exozones. Superior hemisepta few, blunt, short, thick; inferior hemisepta few, thin, short. Both hemisepta scattered in a zoarium. Spines curved proximally; cysts rare at mesotheca. Exilazooecia few, generally lacking. Monticules irregularly distributed, flat to raised, indistinct; consisting of slightly larger, possible autozooecia.
- Colonies are bifoliate and have ribbon-shaped or explanate forms of growth. They grow from pointed proximal tips. Zooecia at the surfaces of the colonies are aligned in longitudinal ranges which are demarcated by slightly raised zooecial walls of the lateral interspaces. Mesopores and acanthopores are lacking. Zooecia grow from the mesothecal plane at a low angle and form a narrow inner region. Thickening of the zooecial walla at the base of the superior hemispeta marks the beginning of the outer region of the zooecia. The thickened zooecial walls of this outer region have a curved laminate microstructure. The inner zooecial walls lining the zooecial tubes have laminae steeply inclined distally to the surface of the colony. These laminae of the inner walls pass into the broadly curved convex intertonguing laminae of the outer walls. The outer walls are not separated by zooecial boundaries and appear amalgamate.
- Superior hemisepta also have a laminate microstructure which is continuous with the microstructure of the inner zooecial walls. Inferior hemisepta, generally short spines projecting from the mesothecal plane and beneath the superior hemisepta, also have a laminate microstructure which is continuous with the laminae of the mesothecal plane. The mesothecal plane lacks median tubuli. It is composed of the overlapping basal zooecial walls.
- The longitudinal ranges in Ptilodictya are generally separable into two kinds: median longitudinal ranges which extend along the median part of a strap and contain zooecia opening orthogonally to the surface; and lateral longitudinal ranges which lie on each side of the median longitudinal ranges and contain zooecia opening obliquely to the surface.
- Zoarium, a simple, unbranched, lanceolate or falciform frond, narrow or wide, which articulates with a small basal expansion; in the young condition the zoarium consists of longitudinally arranged narrow, oblong-quadrate zooecia, new zooecia of different width and arrangement being added subsequently on each side; walls of vestibules thick, solid, and with a double row of minute dots.
- Genotype.—Flustra lanceolata Lonsdale. Silurian of Europe.
- With the Richmond group assigned to the Silurian, the genus Ptilodictya becomes restricted almost entirely to this period, the single exception being a species in the Lower Devonian of Ontario. Ptilodictya is closely related to Escharopora and differs most obviously in the arrangement of its zooecia in parallel longitudinal rows.