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Tubotuberella dentata
Tubotuberella dentata (Raynaud, 1978, p.395, pl.2, fig.13) Lentin and Vozzhennikova, 1990, p.116. Emendation: Riding, 2012, p.70,72, as Gonyaulacysta dentata.
Originally Tubotuberella, subsequently (and now) Gonyaulacysta.
Holotype: Raynaud, 1978, pl.2, fig.13; Jan du Chêne et al., 1986a, pl.126, figs.1–3, lost according to Riding and Michoux (2013, p.51).
Neotype: Fensome et al., 1996, pl.1, fig.20; Riding, 2012, pl.2, figs.1–2; Riding and Michoux, 2013, pl.1, figs.1–3; designated by Riding and Michoux (2013, p.51–52).
Age: middle-late Callovian.
Original diagnosis of Raynaud (1978, p. 395): A large species. Endophragm ovoid, smooth. Periphragm smooth to finely granulate. Apical horn sharply pointed. Apical and antapical pericoels present. The antapical pericoel is shorter than that of Tubotuberella apatela. Tabulation marked by high crests surmounted by regularly inserted denticles. A precingular archaeopyle and an antapical opening are present (translated by J.B. Riding, June 2011).
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Emended diagnosis and description (Riding, 2012):
Emended diagnosis: A large, highly dorsoventrally-compressed, elongate, bicavate species of Gonyaulacysta which has an angular pentagonal dorsoventral outline and normally bears a prominent apical horn often with a prominent apicular structure. The cingulum is subequatorial. The dorsal and lateral paratabulation is indicated by prominent variably denticulate to occasionally smooth sutural crests which dramatically reduce to discontinuous low, distally smooth ridges on the midventral surface and in the apical region. A periarchaeopyle is not developed, and a circular claustrum is present in the antapical plate.
Emended description: A large, elongate species of Gonyaulacysta which is significantly dorsoventrally compressed. The pericyst has an angular pentagonal outline normally with a prominent, largely hollow, distally pointed apical horn and a consistently truncated antapex. The distal part of the apical horn is frequently surmounted by a short (2 to 5 μm), solid apicular structure. The epicyst and hypocyst are broadly similar in overall length. The epicyst is subtriangular with straight sides. The hypocyst is quadrangular with straight to slightly convex sides; the antapical side is by far the shortest. The endocyst is elongate ovoidal to rounded subpentagonal to subhexangular in outline with no apical or antapical horns or protuberances. The species exhibits a bicavate cyst organisation, and the epipericoel and hypopericoel are both extremely well-developed. The epipericoel is subtriangular and the hypopericoel is subquadrate; both frequently extend equatorially towards the paracingulum. However the periphragm and endophragm normally become closely appressed in the central areas of the epicyst and hypocyst, thus a circumcavate or camocavate cyst organisation is never fully developed. There is typically more wall separation in the hypocyst than in the epicyst. A standard gonyaulacacean tabulation (?2pr, 4’, ?1a, 6”, ?6c, 6”’, 1p, 1””, ? 5 s) is fully indicated by prominent sutural crests (normally 4–5 μm high) on the lateral and dorsal areas of the periphragm and discontinuous low, distally smooth sutural ridges on the midventral side and the apical region of the periphragm. The dorsal and lateral sutural crests are frequently surmounted by small (2–4 μm long) thorn-like gonal and intergonal denticles with pointed, truncate or bifurcate distal terminations, or they may be distally smooth. The denticles are normally densest and most prominent around the cingulum, on the hypocyst and especially around the antapex. The denticles may be absent or significantly reduced and this phenomenon, where developed, is typical of the epicyst. The plate boundaries of the antapical (1””) plate are frequently marked by extremely prominent gonal denticles up to 12 μm long. The prominent dorsal and lateral parasutural crests reduce sharply to low, distally smooth ridges on and around the apical horn. The apical edges of the sutural crests on the epicyst are distinctly concave in an apical direction. This marked change in morphology imparts a highly distinctive outline to the apical part of the epicyst, close to the apical part of the endocyst, which frequently has the superficial appearance of having two small horns on either side of the main apical horn in dorsoventral view. A prominent laevorotatory equatorial cingulum 3–5 μm in height is present, and the dorsal cingular crests are relatively prominent. The cingulum is apparently undivided. The laevorotatory nature of the cingulum is often diffi- cult to discern due to the reduced and discontinuous nature of the sutural ornamentation on the midventral surface. Similarly, the sulcus is not prominent because the midventral sutural ridges are low and may be locally suppressed. The sulcus is apparently undivided. The periphragm is relatively thin, and is smooth to shagreenate. The endophragm is relatively thick, smooth to shagreenate, occasionally locally microscabrate. The single-plate (3”) precingular endoarchaeopyle is prominent and the free endoperculum is frequently displaced within the endocyst. A periarchaeopyle is not developed. The antapical (1””) plate is virtually entirely represented by a subcircular claustrum.
Dimensions: The specimens measured here are all from sample DUN 42 (BGS registration number MPA 14067) which was collected from the lowermost Oxfordian succession of the Dunans Clay Member of the Staffin Shale Formation at Dunans, north of Staffin Bay, Isle of Skye, northwest Scotland (Fig. 1). The 10 parameters below are quoted in micrometres (μm) from 38 specimens. The three figures represent the minimum, mean (in parentheses) and maximum respectively. All these size data are presented in Table 1. Note that preservational factors and additional dorsoventral compression may have slightly distorted some of these measurements. Gonyaulacysta dentata is a particularly large Jurassic dinoflagellate cyst. It is ‘large’ (i.e. >100 μm) as defined by Stover and Evitt (1978, p. 5), hence is easy to identify using relatively low magnifications. Helenes and Lucas-Clark (1997, p. 176) commented that the total length of Gonyaulacysta is between 70 to 100 μm, hence Gonyaulacysta dentata is unusually large for this genus.
Length of pericyst including apical horn and denticles: 89 (110) 133
Length of apical horn including apicular structure: 4 (10) 16
Length of epipericoel including apical horn: 11 (19) 24
Length of epipericyst including apical horn, excluding cingulum: 38 (49) 69
Length of hypopericyst including denticles, excluding cingulum: 42 (59) 73
Length of hypopericoel including antapical denticles: 9 (18) 27
Equatorial width of pericyst including cingular denticles: 56 (72) 89
Dorsoventral antapical width of pericyst: 13 (26) 36
Length of endocyst: 53 (72) 84
Equatorial width of endocyst: 42 (60) 73
Raynaud (1978, p. 395) reported that the holotype of Gonyaulacysta dentata is 140 μm long and 92 μm wide, and further noted that the size variation in the type material is 136 to 170 μm by 90 to 96 μm. This compares to 89 to 133 μm by 56 to 89 μm herein (see above). Clearly this is a major disparity; this may be due to microscope calibration issues with the type material and/or swelling effects caused during the laboratory preparation of the sample material of Raynaud (1978). Glycerine jelly and alkali solutions are known to cause palynomorphs to increase in size (e.g. Andersen, 1960; Bruch and Pross, 1999 respectively), and pressure between the microscope slide and coverslip can have similar effects (Cushing, 1961) The measurements by Raynaud (1978) are deemed to be anomalously large because the dimensions quoted by other authors such as Johnson and Hills (1973, p. 206), Kunz (1990, p. 25) and Gedl (2008a, p. 225) are closely comparable to those herein.
Remarks: The large size, characteristic elongate subpentagonal outline and the prominent variably denticulate dorsal and lateral sutural crests of Gonyaulacysta dentata make this species very easy to identify (Fig. 2). One of the most characteristic morphological features of Gonyaulacysta dentata is the disparate heights of the dorsal and lateral sutural crests and the lower, partially discontinuous midventral and apical sutural ridges. This phenomenon has also been observed in Gonyaulacysta jurassica (see Stover and Evitt, 1978, p. 277), but otherwise is highly unusual. The tabulation pattern apparently conforms to that described by Helenes and Lucas-Clark (1997) for Gonyaulacysta, although the second preapical plate (2pr) and the single anterior intercalary plate (1a) have not been unequivocally observed. This species is one of the largest Jurassic dinoflagellate cysts and was originally placed into the genus Tubotuberella Vozzhennikova 1967 by Raynaud (1978). It was subsequently transferred into Gonyaulacysta by Lentin and Vozzhennikova (1990, p. 116), where it is retained herein. Some authors such as Smelror (1993), Birkenmajer and Gedl (2007) and Gedl (2008b) have continued to use the name Tubotuberella dentata. Both Gonyaulacysta and Tubotuberella are elongate, subpentagonal, cavate gonyaulacacean genera which are prominent in the Jurassic. However Tubotuberella is consistently bicavate, with a prominent hypopericoel, and always exhibits an antapical claustrum. It also lacks the strongly denticulate sutural crests which are typical of Gonyaulacysta (see Lentin and Vozzhennikova, 1990, p. 116). The species of Tubotuberella which is most similar to Gonyaulacysta is Tubotuberella dangeardii because the sutural ridges frequently are surmounted by widely spaced short denticles (e.g. Riding and Thomas, 1992, pl. 2.11, fig. 3). Similarly, one of the species of Gonyaulacysta which is most similar to Tubotuberella is Gonyaulacysta eisenackii because of the antapical claustrum and the bicavate cyst organisation. Due to these morphological considerations, Gonyaulacysta eisenackii and Tubotuberella dangeardii may be considered to be intermediate species between Gonyaulacysta and Tubotuberella. For example, the presence of denticulate sutural crests in Gonyaulacysta is not exclusive; the species Gonyaulacysta dualis (Brideaux & Fisher 1976) Stover & Evitt 1978 typically has distally smooth sutural crests which only rarely bear low-relief denticles (Brideaux and Fisher, 1976, p. 18–19). However these two closely related, typically Jurassic, genera are maintained herein despite the strong morphological similarities between them. It is noted, however, that some species of Gonyaulacysta are characterised by unusually large epicysts, where the cingulum is significantly closer to the antapex than the apex (Stover and Evitt, 1978, p. 275–279). These comprise Gonyaulacysta ceratophora (Cookson & Eisenack 1960) Riding 2005, Gonyaulacysta dualis, Gonyaulacysta fenestrata Riding & Helby 2001 and Gonyaulacysta jurassica. These differ from other species such as Gonyaulacysta centriconnata, Gonyaulacysta dentata and Gonyaulacysta eisenackii, which all have equatorial cingulums. Gonyaulacysta dentata exhibits some intraspecific variability. The apical horn is highly variable in length (Table 1), and the apicular structure may be prominent or very small. The antapical breadth of the hypopericoel also varies significantly (Table 1). The overall width also differs, with relatively broad forms (Plate I, figs. 1–3 and Plate II, figs. 1, 2) and elongate, slender morphotypes (Plate I, figs. 4–6) observed. The majority of specimens are relatively broad, and the holotype is one of these wide morphotypes (Raynaud, 1978, pl. 2, fig. 13; Fig. 2, Plate II). The density, length and morphology of the sutural denticles are all somewhat variable, particularly on the epicyst. In some individuals, many of the sutural crests can be relatively smooth distally. Furthermore, the size of the endocyst is relatively inconstant. In some specimens it occupies a greater part of the pericyst than others. A description of Gonyaulacysta dentata was given by Gedl (2008a, p. 225) but this did not constitute a formal emendation. Gonyaulacysta dentata is emended herein to note several important features which were not mentioned by Raynaud (1978). These include the elongate pentagonal outline in dorsoventral view, the apicular structure, the bicavate cyst organisation, the morphological variability of the sutural denticles, the disparate nature of the dorsal and lateral, and midventral sutural ornamentation and the lack of a periarchaeopyle. Furthermore, the emended diagnosis and description note that the prominent denticulate dorsal sutural crests sharply reduce in height to low, distally smooth sutural ridges on and around the apical horn. The apically concave anterior edges of the sutural crests below the apical horn on the epicyst are extremely distinctive. This phenomenon is also developed in Gonyaulacysta eisenackii (see e.g. Beju, 1971, pl. 1, figs. 4–6; Riding, 1987, fig. 9.14) and other gonyaulacacean taxa.
Comparison: The most similar species to Gonyaulacysta dentata is Gonyaulacysta eisenackii in that this taxon has prominent denticulate sutural crests which do not extend to the apical horn. However, Gonyaulacysta eisenackii is significantly smaller (typically around 80 μm in length) than Gonyaulacysta dentata. Furthermore, the former is not as elongate as the latter, and has relatively small pericoels and a small apical horn which lacks an apicular structure (Deflandre, 1938, pl. VI, figs. 7–10). The cingulum of Gonyaulacysta dentata is equatorial, which contrasts markedly with the antapically offset cingulums of Gonyaulacysta ceratophora, Gonyaulacysta dualis, Gonyaulacysta fenestrata and Gonyaulacysta jurassica. Gonyaulacysta dentata is also larger and more denticulate than Tubotuberella dangeardii and other species of this genus (Jan du Chêne et al., 1986, pl. 123).
Originally Tubotuberella, subsequently (and now) Gonyaulacysta.
Holotype: Raynaud, 1978, pl.2, fig.13; Jan du Chêne et al., 1986a, pl.126, figs.1–3, lost according to Riding and Michoux (2013, p.51).
Neotype: Fensome et al., 1996, pl.1, fig.20; Riding, 2012, pl.2, figs.1–2; Riding and Michoux, 2013, pl.1, figs.1–3; designated by Riding and Michoux (2013, p.51–52).
Age: middle-late Callovian.
Original diagnosis of Raynaud (1978, p. 395): A large species. Endophragm ovoid, smooth. Periphragm smooth to finely granulate. Apical horn sharply pointed. Apical and antapical pericoels present. The antapical pericoel is shorter than that of Tubotuberella apatela. Tabulation marked by high crests surmounted by regularly inserted denticles. A precingular archaeopyle and an antapical opening are present (translated by J.B. Riding, June 2011).
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Emended diagnosis and description (Riding, 2012):
Emended diagnosis: A large, highly dorsoventrally-compressed, elongate, bicavate species of Gonyaulacysta which has an angular pentagonal dorsoventral outline and normally bears a prominent apical horn often with a prominent apicular structure. The cingulum is subequatorial. The dorsal and lateral paratabulation is indicated by prominent variably denticulate to occasionally smooth sutural crests which dramatically reduce to discontinuous low, distally smooth ridges on the midventral surface and in the apical region. A periarchaeopyle is not developed, and a circular claustrum is present in the antapical plate.
Emended description: A large, elongate species of Gonyaulacysta which is significantly dorsoventrally compressed. The pericyst has an angular pentagonal outline normally with a prominent, largely hollow, distally pointed apical horn and a consistently truncated antapex. The distal part of the apical horn is frequently surmounted by a short (2 to 5 μm), solid apicular structure. The epicyst and hypocyst are broadly similar in overall length. The epicyst is subtriangular with straight sides. The hypocyst is quadrangular with straight to slightly convex sides; the antapical side is by far the shortest. The endocyst is elongate ovoidal to rounded subpentagonal to subhexangular in outline with no apical or antapical horns or protuberances. The species exhibits a bicavate cyst organisation, and the epipericoel and hypopericoel are both extremely well-developed. The epipericoel is subtriangular and the hypopericoel is subquadrate; both frequently extend equatorially towards the paracingulum. However the periphragm and endophragm normally become closely appressed in the central areas of the epicyst and hypocyst, thus a circumcavate or camocavate cyst organisation is never fully developed. There is typically more wall separation in the hypocyst than in the epicyst. A standard gonyaulacacean tabulation (?2pr, 4’, ?1a, 6”, ?6c, 6”’, 1p, 1””, ? 5 s) is fully indicated by prominent sutural crests (normally 4–5 μm high) on the lateral and dorsal areas of the periphragm and discontinuous low, distally smooth sutural ridges on the midventral side and the apical region of the periphragm. The dorsal and lateral sutural crests are frequently surmounted by small (2–4 μm long) thorn-like gonal and intergonal denticles with pointed, truncate or bifurcate distal terminations, or they may be distally smooth. The denticles are normally densest and most prominent around the cingulum, on the hypocyst and especially around the antapex. The denticles may be absent or significantly reduced and this phenomenon, where developed, is typical of the epicyst. The plate boundaries of the antapical (1””) plate are frequently marked by extremely prominent gonal denticles up to 12 μm long. The prominent dorsal and lateral parasutural crests reduce sharply to low, distally smooth ridges on and around the apical horn. The apical edges of the sutural crests on the epicyst are distinctly concave in an apical direction. This marked change in morphology imparts a highly distinctive outline to the apical part of the epicyst, close to the apical part of the endocyst, which frequently has the superficial appearance of having two small horns on either side of the main apical horn in dorsoventral view. A prominent laevorotatory equatorial cingulum 3–5 μm in height is present, and the dorsal cingular crests are relatively prominent. The cingulum is apparently undivided. The laevorotatory nature of the cingulum is often diffi- cult to discern due to the reduced and discontinuous nature of the sutural ornamentation on the midventral surface. Similarly, the sulcus is not prominent because the midventral sutural ridges are low and may be locally suppressed. The sulcus is apparently undivided. The periphragm is relatively thin, and is smooth to shagreenate. The endophragm is relatively thick, smooth to shagreenate, occasionally locally microscabrate. The single-plate (3”) precingular endoarchaeopyle is prominent and the free endoperculum is frequently displaced within the endocyst. A periarchaeopyle is not developed. The antapical (1””) plate is virtually entirely represented by a subcircular claustrum.
Dimensions: The specimens measured here are all from sample DUN 42 (BGS registration number MPA 14067) which was collected from the lowermost Oxfordian succession of the Dunans Clay Member of the Staffin Shale Formation at Dunans, north of Staffin Bay, Isle of Skye, northwest Scotland (Fig. 1). The 10 parameters below are quoted in micrometres (μm) from 38 specimens. The three figures represent the minimum, mean (in parentheses) and maximum respectively. All these size data are presented in Table 1. Note that preservational factors and additional dorsoventral compression may have slightly distorted some of these measurements. Gonyaulacysta dentata is a particularly large Jurassic dinoflagellate cyst. It is ‘large’ (i.e. >100 μm) as defined by Stover and Evitt (1978, p. 5), hence is easy to identify using relatively low magnifications. Helenes and Lucas-Clark (1997, p. 176) commented that the total length of Gonyaulacysta is between 70 to 100 μm, hence Gonyaulacysta dentata is unusually large for this genus.
Length of pericyst including apical horn and denticles: 89 (110) 133
Length of apical horn including apicular structure: 4 (10) 16
Length of epipericoel including apical horn: 11 (19) 24
Length of epipericyst including apical horn, excluding cingulum: 38 (49) 69
Length of hypopericyst including denticles, excluding cingulum: 42 (59) 73
Length of hypopericoel including antapical denticles: 9 (18) 27
Equatorial width of pericyst including cingular denticles: 56 (72) 89
Dorsoventral antapical width of pericyst: 13 (26) 36
Length of endocyst: 53 (72) 84
Equatorial width of endocyst: 42 (60) 73
Raynaud (1978, p. 395) reported that the holotype of Gonyaulacysta dentata is 140 μm long and 92 μm wide, and further noted that the size variation in the type material is 136 to 170 μm by 90 to 96 μm. This compares to 89 to 133 μm by 56 to 89 μm herein (see above). Clearly this is a major disparity; this may be due to microscope calibration issues with the type material and/or swelling effects caused during the laboratory preparation of the sample material of Raynaud (1978). Glycerine jelly and alkali solutions are known to cause palynomorphs to increase in size (e.g. Andersen, 1960; Bruch and Pross, 1999 respectively), and pressure between the microscope slide and coverslip can have similar effects (Cushing, 1961) The measurements by Raynaud (1978) are deemed to be anomalously large because the dimensions quoted by other authors such as Johnson and Hills (1973, p. 206), Kunz (1990, p. 25) and Gedl (2008a, p. 225) are closely comparable to those herein.
Remarks: The large size, characteristic elongate subpentagonal outline and the prominent variably denticulate dorsal and lateral sutural crests of Gonyaulacysta dentata make this species very easy to identify (Fig. 2). One of the most characteristic morphological features of Gonyaulacysta dentata is the disparate heights of the dorsal and lateral sutural crests and the lower, partially discontinuous midventral and apical sutural ridges. This phenomenon has also been observed in Gonyaulacysta jurassica (see Stover and Evitt, 1978, p. 277), but otherwise is highly unusual. The tabulation pattern apparently conforms to that described by Helenes and Lucas-Clark (1997) for Gonyaulacysta, although the second preapical plate (2pr) and the single anterior intercalary plate (1a) have not been unequivocally observed. This species is one of the largest Jurassic dinoflagellate cysts and was originally placed into the genus Tubotuberella Vozzhennikova 1967 by Raynaud (1978). It was subsequently transferred into Gonyaulacysta by Lentin and Vozzhennikova (1990, p. 116), where it is retained herein. Some authors such as Smelror (1993), Birkenmajer and Gedl (2007) and Gedl (2008b) have continued to use the name Tubotuberella dentata. Both Gonyaulacysta and Tubotuberella are elongate, subpentagonal, cavate gonyaulacacean genera which are prominent in the Jurassic. However Tubotuberella is consistently bicavate, with a prominent hypopericoel, and always exhibits an antapical claustrum. It also lacks the strongly denticulate sutural crests which are typical of Gonyaulacysta (see Lentin and Vozzhennikova, 1990, p. 116). The species of Tubotuberella which is most similar to Gonyaulacysta is Tubotuberella dangeardii because the sutural ridges frequently are surmounted by widely spaced short denticles (e.g. Riding and Thomas, 1992, pl. 2.11, fig. 3). Similarly, one of the species of Gonyaulacysta which is most similar to Tubotuberella is Gonyaulacysta eisenackii because of the antapical claustrum and the bicavate cyst organisation. Due to these morphological considerations, Gonyaulacysta eisenackii and Tubotuberella dangeardii may be considered to be intermediate species between Gonyaulacysta and Tubotuberella. For example, the presence of denticulate sutural crests in Gonyaulacysta is not exclusive; the species Gonyaulacysta dualis (Brideaux & Fisher 1976) Stover & Evitt 1978 typically has distally smooth sutural crests which only rarely bear low-relief denticles (Brideaux and Fisher, 1976, p. 18–19). However these two closely related, typically Jurassic, genera are maintained herein despite the strong morphological similarities between them. It is noted, however, that some species of Gonyaulacysta are characterised by unusually large epicysts, where the cingulum is significantly closer to the antapex than the apex (Stover and Evitt, 1978, p. 275–279). These comprise Gonyaulacysta ceratophora (Cookson & Eisenack 1960) Riding 2005, Gonyaulacysta dualis, Gonyaulacysta fenestrata Riding & Helby 2001 and Gonyaulacysta jurassica. These differ from other species such as Gonyaulacysta centriconnata, Gonyaulacysta dentata and Gonyaulacysta eisenackii, which all have equatorial cingulums. Gonyaulacysta dentata exhibits some intraspecific variability. The apical horn is highly variable in length (Table 1), and the apicular structure may be prominent or very small. The antapical breadth of the hypopericoel also varies significantly (Table 1). The overall width also differs, with relatively broad forms (Plate I, figs. 1–3 and Plate II, figs. 1, 2) and elongate, slender morphotypes (Plate I, figs. 4–6) observed. The majority of specimens are relatively broad, and the holotype is one of these wide morphotypes (Raynaud, 1978, pl. 2, fig. 13; Fig. 2, Plate II). The density, length and morphology of the sutural denticles are all somewhat variable, particularly on the epicyst. In some individuals, many of the sutural crests can be relatively smooth distally. Furthermore, the size of the endocyst is relatively inconstant. In some specimens it occupies a greater part of the pericyst than others. A description of Gonyaulacysta dentata was given by Gedl (2008a, p. 225) but this did not constitute a formal emendation. Gonyaulacysta dentata is emended herein to note several important features which were not mentioned by Raynaud (1978). These include the elongate pentagonal outline in dorsoventral view, the apicular structure, the bicavate cyst organisation, the morphological variability of the sutural denticles, the disparate nature of the dorsal and lateral, and midventral sutural ornamentation and the lack of a periarchaeopyle. Furthermore, the emended diagnosis and description note that the prominent denticulate dorsal sutural crests sharply reduce in height to low, distally smooth sutural ridges on and around the apical horn. The apically concave anterior edges of the sutural crests below the apical horn on the epicyst are extremely distinctive. This phenomenon is also developed in Gonyaulacysta eisenackii (see e.g. Beju, 1971, pl. 1, figs. 4–6; Riding, 1987, fig. 9.14) and other gonyaulacacean taxa.
Comparison: The most similar species to Gonyaulacysta dentata is Gonyaulacysta eisenackii in that this taxon has prominent denticulate sutural crests which do not extend to the apical horn. However, Gonyaulacysta eisenackii is significantly smaller (typically around 80 μm in length) than Gonyaulacysta dentata. Furthermore, the former is not as elongate as the latter, and has relatively small pericoels and a small apical horn which lacks an apicular structure (Deflandre, 1938, pl. VI, figs. 7–10). The cingulum of Gonyaulacysta dentata is equatorial, which contrasts markedly with the antapically offset cingulums of Gonyaulacysta ceratophora, Gonyaulacysta dualis, Gonyaulacysta fenestrata and Gonyaulacysta jurassica. Gonyaulacysta dentata is also larger and more denticulate than Tubotuberella dangeardii and other species of this genus (Jan du Chêne et al., 1986, pl. 123).