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Spinidinium essoi
Spinidinium essoi Cookson and Eisenack, 1967
Originally (and now) Spinidinium, subsequently Magallanesium. Sluijs et al. (2009, p.47) retained this species in Spinidinium.
Holotype: Cookson and Eisenack, 1967, pl.19, fig.1-2
Paratype: Cookson and Eisenack, 1967
Locus typicus: Strahan, Tasmania
Stratum typicum: Paleocene
Original descrpition: Cookson and Eisenack, 1967, p.135
Shell small, somewhat flattened and oval in outline, with straight to convex sides, a relatively broad, circular, equatorial girdle with high ledges bearing short thin spines, a short blunt apical horn and a single sharply-pointed horn on the left-hand side of the antapex. Both surfaces of the shell are partially tabulated, the areas being delimited by short spines. On the ventral surface of the epitheca a small, roughly rectangular area outlined by small dot-like thickenings is usually clearly evident, and a relatively wide furrow-like region, delimited by small spines, is typically present in the hypotheca. An intercalary, trapezoidal archeopyle is developed on the dorsal surface of the epitheca.
In one specimen (Pl. 19, fig. 8) a relatively thin-walled cyst-like body, circular in outline, occupies approximately three-quarters of the cavity of the shell.
The wall of the shell, which is rather sparsely ornamented with pointed or knobbed spines, appears to consist of two closely opposed layers which separate from one another only at or near the bases of the horns, the position of the diaphragnum varying in individual specimens. The apical horn tends to be straightsided and its apex incurved; the antapical horn, which tapers to a sharp point, bears a few downwardly directed spines.
Dimensions: Holotype--overall length 60 µm, width 46 µm, girdle 5 µm wide. Range--overall length c. 50-62 µm, width 40-52 µm, spines up to c. 3 µm.
Affinities:
Cookson and Eisenack, 1967, p.135: S. essoi differs from the Australian Cretaceous species S. styloniferum Cookson and Eisenack 1962 in the shape of the shell, the less numerous and finer spines, the presence of a simple form of tabulation and the shape of the archeopyle. It differs from the two American Paleocene species S. densispinatum and S. microceratum described by Stanley (1965) in the absence of a second antapical horn and, as far as can be judged from the illustrations of both species, the more regular and wider distribution of the spines.
Originally (and now) Spinidinium, subsequently Magallanesium. Sluijs et al. (2009, p.47) retained this species in Spinidinium.
Holotype: Cookson and Eisenack, 1967, pl.19, fig.1-2
Paratype: Cookson and Eisenack, 1967
Locus typicus: Strahan, Tasmania
Stratum typicum: Paleocene
Original descrpition: Cookson and Eisenack, 1967, p.135
Shell small, somewhat flattened and oval in outline, with straight to convex sides, a relatively broad, circular, equatorial girdle with high ledges bearing short thin spines, a short blunt apical horn and a single sharply-pointed horn on the left-hand side of the antapex. Both surfaces of the shell are partially tabulated, the areas being delimited by short spines. On the ventral surface of the epitheca a small, roughly rectangular area outlined by small dot-like thickenings is usually clearly evident, and a relatively wide furrow-like region, delimited by small spines, is typically present in the hypotheca. An intercalary, trapezoidal archeopyle is developed on the dorsal surface of the epitheca.
In one specimen (Pl. 19, fig. 8) a relatively thin-walled cyst-like body, circular in outline, occupies approximately three-quarters of the cavity of the shell.
The wall of the shell, which is rather sparsely ornamented with pointed or knobbed spines, appears to consist of two closely opposed layers which separate from one another only at or near the bases of the horns, the position of the diaphragnum varying in individual specimens. The apical horn tends to be straightsided and its apex incurved; the antapical horn, which tapers to a sharp point, bears a few downwardly directed spines.
Dimensions: Holotype--overall length 60 µm, width 46 µm, girdle 5 µm wide. Range--overall length c. 50-62 µm, width 40-52 µm, spines up to c. 3 µm.
Affinities:
Cookson and Eisenack, 1967, p.135: S. essoi differs from the Australian Cretaceous species S. styloniferum Cookson and Eisenack 1962 in the shape of the shell, the less numerous and finer spines, the presence of a simple form of tabulation and the shape of the archeopyle. It differs from the two American Paleocene species S. densispinatum and S. microceratum described by Stanley (1965) in the absence of a second antapical horn and, as far as can be judged from the illustrations of both species, the more regular and wider distribution of the spines.