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Jansonia
From Williams et al., 2017:
[Jansonia, Pocock, 1972, p. 97; Emendation: Riding and Walton in Riding et al., 1991, p. 146, 148
Type species: Jansonia jurassica, Pocock, 1972 (pl.29, fig.8)]
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Original description: [Pocock, 1972]:
Description:
Vesicle small, more or less pear-shaped in out line. Epitheca terminated by a smoothly rounded, hollow, apical horn which is normally lost through apical archeopyle formation. Capsule very thin and tightly appressed to outer wall.
Tabulation (?`), 6", 6g, 6```, 0-1P, 1````. Vesicle wall characteristically dark brown.
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Stover and Evitt, 1978, p. 58:
Remark:
Type specimens show reasonable indications of a paracingulum, whereas other expressions of paratabulation are vague, as is evidence for the
presence of two wall layers. Specimens are dark, poorly preserved, with numerous short folds and cracks that could easily be mistaken for ridges or parasutures.
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Emended description:
Riding and Walton in Riding et al., 1991:
Diagnosis:
Proximate, acavate dinoflagellate cysts, ovoidal to angular subovoidal in dorsoventral outline, markedly dorsoventrally compressed. Hypocyst typically slightly longer than epicyst.
Paratabulation not indicated or partiform gonyaulacacean, indicated partially to completely by low parasutural ridges or discontinuous, low-relief ornamentation. Kofoidian paratabulation formula: ?pr, ?4`, ?4a, 7", 7c, 6```, 1p, 1````, ?5s. Paracingulum laevorotatory, prominent and relatively high; paraplate ps also prominent, widening antapically.
Archeopyle combination apical/ anterior intercalary; type (tAtI)a, adnate to as.
Autophragm dark-brown, thinning markedly to the anterior of the principal archeopyle suture; intratabular areas smooth or possessing low-relief ornamentation. Size, small (of Stover and Evitt, 1978).
Remarks:
The new paratabulate species Jansonia manifesta has enabled the authors to emend the generic diagnosis. Jansonia has a partiform gonyaulacacean paratabulation (Evitt, 1985, p. 112-119), possessing the large ps paraplate (Z of Evitt,1985), which is expanded antapically, and the sagittally-positioned 1````/1p parasuture (X/Y of Evitt,1985; 1````/2```` of Below,1987). Both the new species, J. manifesta, and the type species J. jurassica are not placed in any other partiform genera, because of the distinctive dark autophragm, leathery in appearance (see Jansonius, 1986); they also exhibit a marked preference for Middle Jurassic freshwater/brackish paleoenvironments (see Pocock, 1972 and herein).
The genus appears to be susceptible to damage near the antapical region (Jansonius,1986, pl.3, figs.4-6; Plate 8, figs.2,5,6 herein), which indicates a possible fundamental mechanical weakness of the autophragm adjacent to paraplates 1```` and 1p.
[Jansonia, Pocock, 1972, p. 97; Emendation: Riding and Walton in Riding et al., 1991, p. 146, 148
Type species: Jansonia jurassica, Pocock, 1972 (pl.29, fig.8)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Pocock, 1972]:
Description:
Vesicle small, more or less pear-shaped in out line. Epitheca terminated by a smoothly rounded, hollow, apical horn which is normally lost through apical archeopyle formation. Capsule very thin and tightly appressed to outer wall.
Tabulation (?`), 6", 6g, 6```, 0-1P, 1````. Vesicle wall characteristically dark brown.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Stover and Evitt, 1978, p. 58:
Remark:
Type specimens show reasonable indications of a paracingulum, whereas other expressions of paratabulation are vague, as is evidence for the
presence of two wall layers. Specimens are dark, poorly preserved, with numerous short folds and cracks that could easily be mistaken for ridges or parasutures.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Riding and Walton in Riding et al., 1991:
Diagnosis:
Proximate, acavate dinoflagellate cysts, ovoidal to angular subovoidal in dorsoventral outline, markedly dorsoventrally compressed. Hypocyst typically slightly longer than epicyst.
Paratabulation not indicated or partiform gonyaulacacean, indicated partially to completely by low parasutural ridges or discontinuous, low-relief ornamentation. Kofoidian paratabulation formula: ?pr, ?4`, ?4a, 7", 7c, 6```, 1p, 1````, ?5s. Paracingulum laevorotatory, prominent and relatively high; paraplate ps also prominent, widening antapically.
Archeopyle combination apical/ anterior intercalary; type (tAtI)a, adnate to as.
Autophragm dark-brown, thinning markedly to the anterior of the principal archeopyle suture; intratabular areas smooth or possessing low-relief ornamentation. Size, small (of Stover and Evitt, 1978).
Remarks:
The new paratabulate species Jansonia manifesta has enabled the authors to emend the generic diagnosis. Jansonia has a partiform gonyaulacacean paratabulation (Evitt, 1985, p. 112-119), possessing the large ps paraplate (Z of Evitt,1985), which is expanded antapically, and the sagittally-positioned 1````/1p parasuture (X/Y of Evitt,1985; 1````/2```` of Below,1987). Both the new species, J. manifesta, and the type species J. jurassica are not placed in any other partiform genera, because of the distinctive dark autophragm, leathery in appearance (see Jansonius, 1986); they also exhibit a marked preference for Middle Jurassic freshwater/brackish paleoenvironments (see Pocock, 1972 and herein).
The genus appears to be susceptible to damage near the antapical region (Jansonius,1986, pl.3, figs.4-6; Plate 8, figs.2,5,6 herein), which indicates a possible fundamental mechanical weakness of the autophragm adjacent to paraplates 1```` and 1p.