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Placunopsis
Classification
Phylum:
Mollusca
Class:
Bivalvia
Subclass:
Pteriomorphia
Order:
Pterioida
Suborder:
Pteriina
Superfamily:
Pectinacea (scallops and relatives)
Family:
Terquemiidae
Formal Genus Name and Reference:
Placunopsis Morris & LYCETT, 1853, p. 5
Type Species:
P. fibrosa LAUBE, 1867, p. 16
Images
(Click to enlarge in a new window)
Fig. C100,4a-c. ·P. fibrosa (LAUBE), M.Jur.(Bathon.), Eng.; 4a, flat but presumed LV ext., Xl; 4b,c, convex specimen, also presumed to be LV ext., X I, and into of hinge region, arrow pointing to swelling in umbonal cavity, X2.3 (all Cox, n). --Fig. C100,4d. P. plana (GIEBEL), M.Trias. (Muschelkalk), Ger.; specimens sessile on Lima shell, X 1.3 (SE1lacher, 1954).
Synonyms
Geographic Distribution
cosmop.
Age Range
Beginning Stage in Treatise Usage:
M.Trias.
Beginning International Stage:
Anisian
Fraction Up In Beginning Stage:
0
Beginning Date:
246.7
Ending Stage in Treatise Usage:
U.Cret.(Maastricht.)
Ending International Stage:
Maastrichtian
Fraction Up In Ending Stage:
100
Ending Date:
66.04
Description
Rather small, suborbicular or ovate, subequilateral, not auriculate; lower valve (?RV) flat, attached by almost its entire surface when evidence of attachment exists, specimens with smaller attachment areas rare or wanting; upper valve almost flat to strongly inflated, with distinct, not quite marginal umbo, some specimens with allomorphic sculpture derived from shells to which lower valve had grown attached; adductor scar relatively large, not quite median in position; no well-defined cardinal area, ligamental pit or chondrophore; an uneven thickening along the hinge margin may have been cardinal area; irregular transverse ridge or swelling, function of which is uncertain, occupies umbonal cavity of free valve; crura typically absent (note I); ornament of irregular radial threads, barely visible in some species, well developed in others; ostracum foliaceous.
References
Morris, John, \& Lycett, John Morretes, F. L. de, 1853-54, A monograph of the Mollusca from the Great Oolite, chiefly from Minchinhampton and the coast of Yorkshire, part II, Bivalves: Palaeontograph. Soc. London, $147 \mathrm{p} ., 15 \mathrm{pl}$.
Museum or Author Information
Classification
Phylum:
Mollusca
Class:
Bivalvia
Subclass:
Pteriomorphia
Order:
Pterioida
Suborder:
Pteriina
Superfamily:
Pectinacea (scallops and relatives)
Family:
Terquemiidae
Formal Genus Name and Reference:
Placunopsis Morris & LYCETT, 1853, p. 5
Type Species:
P. fibrosa LAUBE, 1867, p. 16
Images
(Click to enlarge in a new window)
Fig. C100,4a-c. ·P. fibrosa (LAUBE), M.Jur.(Bathon.), Eng.; 4a, flat but presumed LV ext., Xl; 4b,c, convex specimen, also presumed to be LV ext., X I, and into of hinge region, arrow pointing to swelling in umbonal cavity, X2.3 (all Cox, n). --Fig. C100,4d. P. plana (GIEBEL), M.Trias. (Muschelkalk), Ger.; specimens sessile on Lima shell, X 1.3 (SE1lacher, 1954).
Synonyms
Geographic Distribution
cosmop.
Age Range
Beginning Stage in Treatise Usage:
M.Trias.
Beginning International Stage:
Anisian
Fraction Up In Beginning Stage:
0
Beginning Date:
246.7
Ending Stage in Treatise Usage:
U.Cret.(Maastricht.)
Ending International Stage:
Maastrichtian
Fraction Up In Ending Stage:
100
Ending Date:
66.04
Description
Rather small, suborbicular or ovate, subequilateral, not auriculate; lower valve (?RV) flat, attached by almost its entire surface when evidence of attachment exists, specimens with smaller attachment areas rare or wanting; upper valve almost flat to strongly inflated, with distinct, not quite marginal umbo, some specimens with allomorphic sculpture derived from shells to which lower valve had grown attached; adductor scar relatively large, not quite median in position; no well-defined cardinal area, ligamental pit or chondrophore; an uneven thickening along the hinge margin may have been cardinal area; irregular transverse ridge or swelling, function of which is uncertain, occupies umbonal cavity of free valve; crura typically absent (note I); ornament of irregular radial threads, barely visible in some species, well developed in others; ostracum foliaceous.
References
Morris, John, \& Lycett, John Morretes, F. L. de, 1853-54, A monograph of the Mollusca from the Great Oolite, chiefly from Minchinhampton and the coast of Yorkshire, part II, Bivalves: Palaeontograph. Soc. London, $147 \mathrm{p} ., 15 \mathrm{pl}$.