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Alisocysta ornata
From Fensome et al., 2019:
Alisocysta ornata, (Cookson and Eisenack, 1965a, p.124, pl.13, figs.1–8) Stover and Evitt, 1978, p.16.
Holotype: Cookson and Eisenack, 1965a, pl.13, figs.1–2.
NOW Stoveracysta.
Originally Eisenackia, subsequently Alisocysta, thirdly (and now) Stoveracysta.
Age: Late Eocene.
Locus typicus: Southwest Victoria, Australia
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Original description as Eisenackia ornata: [Cookson and Eisenack 1965, p. 124]:
Description:
Shell oval, apex slightly pointed, antapex with two short projections, girdle equatorial, broad, strongly helicoid, divided into six plates. Dorsal surface clearly tabulated, the plates which are outlined by low, transparent ledges (Pl.13, fig.8) being separated by distinct furrows. The central field, corresponding to the longitudinal furrow, is broadly oval and crossed by a varying number of irregularly arranged straight or curved low, narrow ridges of different lengths. The two antapical projections are situated at the ventral corners of the antapical plate. The surface of the shell is rather finely and closely granular. The shell opens by the detachment of a slightly hexagonal apical operculum (Pl.13, fig.7).
Tabulation: 4", 5"" (or 6""), 5""", 2p, 1"""".
Dimensions:
Range: width: 55-88 µm.
Affinities:
Eisenackia ornata is clearly distinguishable from the genotype E.crassitabulata Deflandre and Cookson (1955) by the granular surface pattern in contrast to the thick-walled reticulum of E.crassitabulata and by the unplated and distinctive character of its ventral field.
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Emended description as Eisenackia ornata:
Stover, 1975, p.40-41:
Description:
Cysts ellipsoidal; apicalantapical axis longer than equatorial diameter. Cyst wall 1.5 to 2.0 µm thick; outer surface faintly sculptured and with smooth peritabular ridges, 2 to 2.5 µm high and 1 to 1.5 µm wide, usually smooth distal surfaces.
Tabulation as reflected by peritabular ridges gonyaulacacean; formula 4", 6", 6c, 6"", 1p, 1"""", 2-4s, (Text-fig. 5).
Archeopyle apical, Type A, operculum free and detached as single entity consisting of the four reflected apical plates. Plates 1" and 4" somewhat triangular, of similar size, and appreciably smaller than plates 2" and 3", of which the former is larger (Pl. 2, fig. 6; Text-fig. 5). Outline of archeopyle margin zigzag, with a deep sulcal notch.
In the precingular series, the area outlined by the peritabular ridge on reflected plate 6" is about equidimensional, whereas areas on plates 2" to 5" are wider than high; on plate 1" the ridge outlines a triangular area with bluntly rounded apex adjacent to sulcus (Pl. 2, fig. 7c). Ridges on the 6 cingular plates may be discontinuous and commonly outline narrowly elliptical areas; those on the postcingular plates outline more or less rectangular areas; outline of the peritabular ridge on plate 1p is somewhat triangular while that of the antapical ridge is roundly pentagonal to nearly heart shaped, with a shallow midventral concavity.
In sulcus a narrow, longitudinally elongate, anterior sulcal plate lies immediately posterior to sulcal notch, and a square posterior sulcal plate occurs at antapical end. In between are 3 additional plates, however, all 3 have not been observed on one specimen. Ridges are almost always discontinuous on these plates whose shapes and locations are: (1) a circular plate immediately anterior to the posterior sulcal plate, (2) an elliptical plate on the left side of the sulcus between the anterior sulcal plate and plate 1p, which is interpreted as representing plate 1""", and (3)a very small circular plate on the right side of the sulcus opposite plate 6c.
Variability:
Except for differences in size, and the presence, absence, and relative completeness of sulcal peritabular ridges, variability among specimens of Eisenackia ornata is slight. Features that are constant or within narrow limits include wall thickness and texturing, the height and width of the peritabular ridges, and the shapes of the areas outlined by the peritabular ridges on nonsulcal plates.
Dimensions:
Complete specimens 63 µm to 73 µm long and 63 µm to 70 µm wide; specimens lacking opercula more common and 60 µm to 66 µm long and 68 µm to 90 µm wide.
Affinities:
On Eisenackia crassitabulata Deflandre and Cookson (1955), reflected plates are indicated by foveolate-reticulate platforms separated by sutural depressions, whereas in E. ornata, the reflected plates are indicated by peritabular ridges, which occur also on E. circumtabulata Drugg (1967). Based on photomicrographs of E. circumtabulata from the Kincaid Formation of Texas, kindly provided by W. R. Evitt together with his interpretation of the reflected tabulation (also see Evitt, 1973, pl. 1, fig. 15), E. circumtabulata is smaller than E. ornata and shows a better development of structures, especially in the ventral area. In addition the peritabular ridges on E. circumtabulata appear to be more sharply defined and better developed than those on E. ornata. Small but potentially important differences in the relative sizes and shapes of the areas outlined by the peritabular ridges may be seen, however, the examination of more specimens of E. circumtabulata is necessary before a meaningful evaluation of these differences can be made.
Superficially Schematophora speciosa resembles Eisenackia ornata. The latter differs in the following respects: (1) cingular series is represented by peritabular ridges that are absent in S. speciosa, (2) all peritabular ridges on E. ornata are separated consistently, whereas those on the operculum and on the ventral surface of S. speciosa tend to merge; (3) distances between ridges are less on E. ornata and (4) average size of E. ornata specimens is larger, although the size ranges of the two species overlap.
Alisocysta ornata, (Cookson and Eisenack, 1965a, p.124, pl.13, figs.1–8) Stover and Evitt, 1978, p.16.
Holotype: Cookson and Eisenack, 1965a, pl.13, figs.1–2.
NOW Stoveracysta.
Originally Eisenackia, subsequently Alisocysta, thirdly (and now) Stoveracysta.
Age: Late Eocene.
Locus typicus: Southwest Victoria, Australia
---------------------------------------------------------------------------------------------------
Original description as Eisenackia ornata: [Cookson and Eisenack 1965, p. 124]:
Description:
Shell oval, apex slightly pointed, antapex with two short projections, girdle equatorial, broad, strongly helicoid, divided into six plates. Dorsal surface clearly tabulated, the plates which are outlined by low, transparent ledges (Pl.13, fig.8) being separated by distinct furrows. The central field, corresponding to the longitudinal furrow, is broadly oval and crossed by a varying number of irregularly arranged straight or curved low, narrow ridges of different lengths. The two antapical projections are situated at the ventral corners of the antapical plate. The surface of the shell is rather finely and closely granular. The shell opens by the detachment of a slightly hexagonal apical operculum (Pl.13, fig.7).
Tabulation: 4", 5"" (or 6""), 5""", 2p, 1"""".
Dimensions:
Range: width: 55-88 µm.
Affinities:
Eisenackia ornata is clearly distinguishable from the genotype E.crassitabulata Deflandre and Cookson (1955) by the granular surface pattern in contrast to the thick-walled reticulum of E.crassitabulata and by the unplated and distinctive character of its ventral field.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description as Eisenackia ornata:
Stover, 1975, p.40-41:
Description:
Cysts ellipsoidal; apicalantapical axis longer than equatorial diameter. Cyst wall 1.5 to 2.0 µm thick; outer surface faintly sculptured and with smooth peritabular ridges, 2 to 2.5 µm high and 1 to 1.5 µm wide, usually smooth distal surfaces.
Tabulation as reflected by peritabular ridges gonyaulacacean; formula 4", 6", 6c, 6"", 1p, 1"""", 2-4s, (Text-fig. 5).
Archeopyle apical, Type A, operculum free and detached as single entity consisting of the four reflected apical plates. Plates 1" and 4" somewhat triangular, of similar size, and appreciably smaller than plates 2" and 3", of which the former is larger (Pl. 2, fig. 6; Text-fig. 5). Outline of archeopyle margin zigzag, with a deep sulcal notch.
In the precingular series, the area outlined by the peritabular ridge on reflected plate 6" is about equidimensional, whereas areas on plates 2" to 5" are wider than high; on plate 1" the ridge outlines a triangular area with bluntly rounded apex adjacent to sulcus (Pl. 2, fig. 7c). Ridges on the 6 cingular plates may be discontinuous and commonly outline narrowly elliptical areas; those on the postcingular plates outline more or less rectangular areas; outline of the peritabular ridge on plate 1p is somewhat triangular while that of the antapical ridge is roundly pentagonal to nearly heart shaped, with a shallow midventral concavity.
In sulcus a narrow, longitudinally elongate, anterior sulcal plate lies immediately posterior to sulcal notch, and a square posterior sulcal plate occurs at antapical end. In between are 3 additional plates, however, all 3 have not been observed on one specimen. Ridges are almost always discontinuous on these plates whose shapes and locations are: (1) a circular plate immediately anterior to the posterior sulcal plate, (2) an elliptical plate on the left side of the sulcus between the anterior sulcal plate and plate 1p, which is interpreted as representing plate 1""", and (3)a very small circular plate on the right side of the sulcus opposite plate 6c.
Variability:
Except for differences in size, and the presence, absence, and relative completeness of sulcal peritabular ridges, variability among specimens of Eisenackia ornata is slight. Features that are constant or within narrow limits include wall thickness and texturing, the height and width of the peritabular ridges, and the shapes of the areas outlined by the peritabular ridges on nonsulcal plates.
Dimensions:
Complete specimens 63 µm to 73 µm long and 63 µm to 70 µm wide; specimens lacking opercula more common and 60 µm to 66 µm long and 68 µm to 90 µm wide.
Affinities:
On Eisenackia crassitabulata Deflandre and Cookson (1955), reflected plates are indicated by foveolate-reticulate platforms separated by sutural depressions, whereas in E. ornata, the reflected plates are indicated by peritabular ridges, which occur also on E. circumtabulata Drugg (1967). Based on photomicrographs of E. circumtabulata from the Kincaid Formation of Texas, kindly provided by W. R. Evitt together with his interpretation of the reflected tabulation (also see Evitt, 1973, pl. 1, fig. 15), E. circumtabulata is smaller than E. ornata and shows a better development of structures, especially in the ventral area. In addition the peritabular ridges on E. circumtabulata appear to be more sharply defined and better developed than those on E. ornata. Small but potentially important differences in the relative sizes and shapes of the areas outlined by the peritabular ridges may be seen, however, the examination of more specimens of E. circumtabulata is necessary before a meaningful evaluation of these differences can be made.
Superficially Schematophora speciosa resembles Eisenackia ornata. The latter differs in the following respects: (1) cingular series is represented by peritabular ridges that are absent in S. speciosa, (2) all peritabular ridges on E. ornata are separated consistently, whereas those on the operculum and on the ventral surface of S. speciosa tend to merge; (3) distances between ridges are less on E. ornata and (4) average size of E. ornata specimens is larger, although the size ranges of the two species overlap.