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Diphasiosphaera extrema
Plate 18, Figs. 1-12
Hystrichostrogylon sp. HARDING 1990, p. 30, pl. 12, figs. 12-14
Holotype: Plate 18, Figures 1, 2, 5
Paratype: Plate 18, Figures 3, 6, 9
Type Locality: early Barremian, Speeton Clay Formation, rarocinctum ammonite Zone. Holotype: Slide LB5D(III), E.F. U41.4. Paratype: Slide LB4D(4), E.F. D47.1.
Derivation of Name: From the Latin extremus, extreme, utmost- in reference to the highly cavate nature of this species.
Diagnosis: A species with a smooth, ovoidal endocyst and a thinner, smooth to very finely granular, spheroidal pericyst. Wall layers are separate over much of the cyst with ventral and hypocystal cavation particularly pronounced. The pericyst displays low sutural features, each formed of a crest bearing a double row of numerous short spines; the spines may be flat-ended or acuminate, particularly around cingular margins. A short, distally open, parallel-sided to broadly-tapering apical horn is invariably present, flat-ended or bearing short spines at its distal extreme. The archeopyle is single plate precingular (3").
Dimensions: Holotype: Endocyst Length - 51 μm,Width - 48 μm.
Pericyst Length - 63 μm, Width - 68 μm.
Paratype: Endocyst Length - 56 μm, Width - 48 μm.
Pericyst Length - 73 μm, Width - 76 μm. Overall: Endocyst Length - 63 (55) 51 μm.Width - 58 (52) 48 μm.
Pericyst Length - 84 (74) 63 μm. Width - 81 (74) 68 μm.
Specimens Measured: 11.
Remarks: Diphasiosphaera extrema n. sp. has several characteristics in common with Diphasiosphaera stolidota Duxbury 1980, particularly its apical horn type, its fairly thick, smooth endocyst and cavation. However, the high degree of cavation often leads to significant cyst distortion so that the exact nature of the endocyst/pericyst contact remains unclear, as does the tabulation.
The sutural crests are most unusual in being “double”, with each suture marked by two spine-bearing crests. Duxbury (1980, p. 117), in describing Diphasiosphaera stolidota, stated “Reduction of processes in the more cavate regions involves firstly the loss of process ‘stalks’ so that one may see a double row of spines marking out paraplate boundaries with these spines representing the distal bifurcation of parasutural processes”. However, Diphasiosphaera extrema differs in having crests as well as rows of spines and in the relatively large number of spines per crest.
Diphasiosphaera extrema has a very short range, being restricted to Beds LB5D to LB4D at Speeton, thus within the older part of the early Barremian, rarocinctum ammonite Zone. Harding (1990, p. 30) described this species informally as Hystrichostrogylon sp., stating that it, “has only been found in the lowest Barremian rocks of two of the studied sections (Speeton and Hunstanton)”, although he included it in neither of his stratigraphic summary charts for those two sections. However, Harding’s illustrated specimens were also from Speeton Bed LB5D.
Hystrichostrogylon sp. HARDING 1990, p. 30, pl. 12, figs. 12-14
Holotype: Plate 18, Figures 1, 2, 5
Paratype: Plate 18, Figures 3, 6, 9
Type Locality: early Barremian, Speeton Clay Formation, rarocinctum ammonite Zone. Holotype: Slide LB5D(III), E.F. U41.4. Paratype: Slide LB4D(4), E.F. D47.1.
Derivation of Name: From the Latin extremus, extreme, utmost- in reference to the highly cavate nature of this species.
Diagnosis: A species with a smooth, ovoidal endocyst and a thinner, smooth to very finely granular, spheroidal pericyst. Wall layers are separate over much of the cyst with ventral and hypocystal cavation particularly pronounced. The pericyst displays low sutural features, each formed of a crest bearing a double row of numerous short spines; the spines may be flat-ended or acuminate, particularly around cingular margins. A short, distally open, parallel-sided to broadly-tapering apical horn is invariably present, flat-ended or bearing short spines at its distal extreme. The archeopyle is single plate precingular (3").
Dimensions: Holotype: Endocyst Length - 51 μm,Width - 48 μm.
Pericyst Length - 63 μm, Width - 68 μm.
Paratype: Endocyst Length - 56 μm, Width - 48 μm.
Pericyst Length - 73 μm, Width - 76 μm. Overall: Endocyst Length - 63 (55) 51 μm.Width - 58 (52) 48 μm.
Pericyst Length - 84 (74) 63 μm. Width - 81 (74) 68 μm.
Specimens Measured: 11.
Remarks: Diphasiosphaera extrema n. sp. has several characteristics in common with Diphasiosphaera stolidota Duxbury 1980, particularly its apical horn type, its fairly thick, smooth endocyst and cavation. However, the high degree of cavation often leads to significant cyst distortion so that the exact nature of the endocyst/pericyst contact remains unclear, as does the tabulation.
The sutural crests are most unusual in being “double”, with each suture marked by two spine-bearing crests. Duxbury (1980, p. 117), in describing Diphasiosphaera stolidota, stated “Reduction of processes in the more cavate regions involves firstly the loss of process ‘stalks’ so that one may see a double row of spines marking out paraplate boundaries with these spines representing the distal bifurcation of parasutural processes”. However, Diphasiosphaera extrema differs in having crests as well as rows of spines and in the relatively large number of spines per crest.
Diphasiosphaera extrema has a very short range, being restricted to Beds LB5D to LB4D at Speeton, thus within the older part of the early Barremian, rarocinctum ammonite Zone. Harding (1990, p. 30) described this species informally as Hystrichostrogylon sp., stating that it, “has only been found in the lowest Barremian rocks of two of the studied sections (Speeton and Hunstanton)”, although he included it in neither of his stratigraphic summary charts for those two sections. However, Harding’s illustrated specimens were also from Speeton Bed LB5D.