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Stanfordella perculta
Plate 22, Figures 1-8
Holotype: Plate 22, Figures 5, 6
Paratype: Plate 22, Figure 1, 4, 8
Type Locality: Speeton Clay Formation, early Hauterivian. Bed C11B, regale ammonite Zone. Holotype: Slide midC11B(4), E.F. J52.1. Paratype: Slide midC11B(1), E.F. D34.0.
Derivation of Name: From the Latin percultus, highly adorned – in reference to the elaborate nature of this species.
Diagnosis: A thin-walled species of Stanfordella without obvious surface ornament. Ashort, blunt apical horn is present. Tab-ulation 4', 6", 6c, 6"', lp, 1p.v., 1"" with an S-type ventral plate arrangement is outlined by regularly perforate sutural crests. Prominent, evenly-spaced, spines run along all sutural crests, although both crests and spines can be reduced adjacent to the sulcus. Individual spines are slender, tapering and usually distally bifurcate in the plane of their supporting crests. Cingulum clearly defined, offset by one cingular width ventrally. Archeopyle single plate mid-dorsal (3").
Dimensions: Holotype: 56 × 58 μm.
Paratype: 53 x53 μm.
Overall: 61 (57) 53 μm × 61 (56) 51 μm
Specimens Measured: 10
Remarks. A 5"/1' (6/1u) contact and a significantly reduced plate 4' are typical of Stanfordella and have allowed this species to be positively assigned to that genus. Stanfordella perculta n. sp. is similar to Stanfordella exsanguia (Duxbury 1977) Helenes and Lucas-Clark 1997 and S. ordocava (Duxbury 1977) Helenes and Lucas-Clark 1997, in being thin walled, without clear surface ornament. It is most similar to the last species in having regularly-spaced perforations along the sutural crests. It differs from both, however, in possessing numerous, regularly-spaced, relatively-long sutural spines. Stanfordella perculta is easily recogniseable, even when broken.
This species is restricted to the early Hauterivian and occurrences tend to be sporadic. It was observed between Beds C11B and C7E at Speeton (regale to inversum ammonite Zones), and it was common in Bed C11B. Ataxon sharing all of the characteristics of S. perculta, but lacking any perforations along sutural crests has been referred here to Stanfordella cf. perculta (Plate 22, Figs. 12, 16). This form was largely restricted to Speeton Beds D2D to D1 (amblygonium to noricum ammonite Zones), immediately predating S. perculta sensu stricto, but with isolated occurrences in Speeton Beds C11A and C7H.
A single specimen of a further taxon similar to S. perculta was recorded in Speeton Bed C7B (latest early Hauterivian, top inversum ammonite Zone), immediately above the LAD of S. perculta sensu stricto and this is informally referred to here as “Stanfordella perculta grp.” (Plate 22, Figs. 10, 13, 14). In this case, the overall morphology is similar to Stanfordella cf. perculta but very slender connections are present, linking the sutural spines medially. This specimen is thicker walled than either S. perculta or S. cf. perculta.
Holotype: Plate 22, Figures 5, 6
Paratype: Plate 22, Figure 1, 4, 8
Type Locality: Speeton Clay Formation, early Hauterivian. Bed C11B, regale ammonite Zone. Holotype: Slide midC11B(4), E.F. J52.1. Paratype: Slide midC11B(1), E.F. D34.0.
Derivation of Name: From the Latin percultus, highly adorned – in reference to the elaborate nature of this species.
Diagnosis: A thin-walled species of Stanfordella without obvious surface ornament. Ashort, blunt apical horn is present. Tab-ulation 4', 6", 6c, 6"', lp, 1p.v., 1"" with an S-type ventral plate arrangement is outlined by regularly perforate sutural crests. Prominent, evenly-spaced, spines run along all sutural crests, although both crests and spines can be reduced adjacent to the sulcus. Individual spines are slender, tapering and usually distally bifurcate in the plane of their supporting crests. Cingulum clearly defined, offset by one cingular width ventrally. Archeopyle single plate mid-dorsal (3").
Dimensions: Holotype: 56 × 58 μm.
Paratype: 53 x53 μm.
Overall: 61 (57) 53 μm × 61 (56) 51 μm
Specimens Measured: 10
Remarks. A 5"/1' (6/1u) contact and a significantly reduced plate 4' are typical of Stanfordella and have allowed this species to be positively assigned to that genus. Stanfordella perculta n. sp. is similar to Stanfordella exsanguia (Duxbury 1977) Helenes and Lucas-Clark 1997 and S. ordocava (Duxbury 1977) Helenes and Lucas-Clark 1997, in being thin walled, without clear surface ornament. It is most similar to the last species in having regularly-spaced perforations along the sutural crests. It differs from both, however, in possessing numerous, regularly-spaced, relatively-long sutural spines. Stanfordella perculta is easily recogniseable, even when broken.
This species is restricted to the early Hauterivian and occurrences tend to be sporadic. It was observed between Beds C11B and C7E at Speeton (regale to inversum ammonite Zones), and it was common in Bed C11B. Ataxon sharing all of the characteristics of S. perculta, but lacking any perforations along sutural crests has been referred here to Stanfordella cf. perculta (Plate 22, Figs. 12, 16). This form was largely restricted to Speeton Beds D2D to D1 (amblygonium to noricum ammonite Zones), immediately predating S. perculta sensu stricto, but with isolated occurrences in Speeton Beds C11A and C7H.
A single specimen of a further taxon similar to S. perculta was recorded in Speeton Bed C7B (latest early Hauterivian, top inversum ammonite Zone), immediately above the LAD of S. perculta sensu stricto and this is informally referred to here as “Stanfordella perculta grp.” (Plate 22, Figs. 10, 13, 14). In this case, the overall morphology is similar to Stanfordella cf. perculta but very slender connections are present, linking the sutural spines medially. This specimen is thicker walled than either S. perculta or S. cf. perculta.