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Gonyaulacysta axicerastes
Gonyaulacysta axicerastes Sarjeant, 1966
Holotype: Sarjeant, 1966, pl.13, figs.11-12; Jan du Chêne et al., 1986, pl.45, figs.6-9
Locus typicus: Speeton Clay, Heslerton, England
Stratum typicum: Middle Barremian
Original diagnosis; Sarjeant, 1966, p.114
A Gonyaulacysta having a spheroidal shell with apical pericoel crowned by slender horn arising from periphragm. Second short hom, formed from both membranes, present at antapex. Tabulation ?4", 1a, 6"", 6c, 6""", 1p, 1""""; plate boundaries bearing high delicate crests. Cingulum and sulcus relatively narrow, sulcus somewhat sinuous and broadening posteriorly.
Dimensions: holotype: overall length 71 Ám, breadth 60 Ám; shell length 50 Ám,
breadth 52 Ám; width of cingulum c.5 Ám; length of apical horn, 8 Ám; length of antapical horn, 7-5 Ám.
Original description: Sarjeant, 1966, p. 115
Shell spheroidal, slightly broader than long, with epitract surmounted by a dome-like outgrowth of the periphragm enclosing an apical pericoel. A slender, furcate horn arises *om the apex. The dome-like structure arises from the confluent crests of the plates on the apical portion of the epitract; position of three -? four apical plates and an anterior intercalary plate are indicated by dimples in this structure. Six precingular plates are present, plate 6"" being of reduced size.
Six postcingular plates are likewise present, with plate 1""" slightly reduced to accommodate the posterior intercalary plate. A polygonal plate occupies the antapex; from its centre arises a short, blunt antapical process. Slender spines at the angles sustain the crests surrounding the antapex; these crests are not connected to the antapical process.
The cingulum forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by more than twice its width. It is divided into six cingular plates. The sulcus is sinuous rather than sigmoidal: a median section along its line would touch the two ends of the cingulum but would not cut them. It is of moderate breadth in its epitractal portion, but widens as it approaches the antapex.
The crests are high and delicate, with denticulate edges; they are irregularly perforate, the perforations being so fine as to be almost imperceptible at high magnifications (x1000). The surface bears an irregular, sparse scatter of coarse tubercles, but is otherwise smooth. No archaeopyle has been observed.
Holotype: Sarjeant, 1966, pl.13, figs.11-12; Jan du Chêne et al., 1986, pl.45, figs.6-9
Locus typicus: Speeton Clay, Heslerton, England
Stratum typicum: Middle Barremian
Original diagnosis; Sarjeant, 1966, p.114
A Gonyaulacysta having a spheroidal shell with apical pericoel crowned by slender horn arising from periphragm. Second short hom, formed from both membranes, present at antapex. Tabulation ?4", 1a, 6"", 6c, 6""", 1p, 1""""; plate boundaries bearing high delicate crests. Cingulum and sulcus relatively narrow, sulcus somewhat sinuous and broadening posteriorly.
Dimensions: holotype: overall length 71 Ám, breadth 60 Ám; shell length 50 Ám,
breadth 52 Ám; width of cingulum c.5 Ám; length of apical horn, 8 Ám; length of antapical horn, 7-5 Ám.
Original description: Sarjeant, 1966, p. 115
Shell spheroidal, slightly broader than long, with epitract surmounted by a dome-like outgrowth of the periphragm enclosing an apical pericoel. A slender, furcate horn arises *om the apex. The dome-like structure arises from the confluent crests of the plates on the apical portion of the epitract; position of three -? four apical plates and an anterior intercalary plate are indicated by dimples in this structure. Six precingular plates are present, plate 6"" being of reduced size.
Six postcingular plates are likewise present, with plate 1""" slightly reduced to accommodate the posterior intercalary plate. A polygonal plate occupies the antapex; from its centre arises a short, blunt antapical process. Slender spines at the angles sustain the crests surrounding the antapex; these crests are not connected to the antapical process.
The cingulum forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by more than twice its width. It is divided into six cingular plates. The sulcus is sinuous rather than sigmoidal: a median section along its line would touch the two ends of the cingulum but would not cut them. It is of moderate breadth in its epitractal portion, but widens as it approaches the antapex.
The crests are high and delicate, with denticulate edges; they are irregularly perforate, the perforations being so fine as to be almost imperceptible at high magnifications (x1000). The surface bears an irregular, sparse scatter of coarse tubercles, but is otherwise smooth. No archaeopyle has been observed.