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Micrhystridium eupeplos
Original description: [Valensi, 1949, p. 542] (translated from French):
Holotype: Bajocian, Croisilles flint (Calvados).
Paratypes: Bajocian, Croisilles flint (Calvados); Bathonian, Lessart flint (Vienne) (flint no. 98); Bathonian, Lessart flint (Vienne) (flint no. 102).
A membrane surrounds the shell, of a regularly spherical shape, attaches to the ends of the processes and draws polygonal fields on the upper face; the processes, about fifteen in number, have the shape of a T with very elongated branches on which this membrane rests. The holotype specimen (1 in fig. 3) has a diameter of 10 μ without the processes and 14 μ including them.
All the individuals observed have a dark brown color.
The paralype of flint 98 (Balhonian of Lessart) (2, 3 of fig. 3)
shows much more numerous processes (about 25), very clear and very regular polygonal fields on the angles of which are inserted the processes, in the form of short, straight and hollow rods, the diameter is 12 μ without the processes and 16 μ with them; the same type is represented in a flint from the Bajocian of Croisilles by a smaller form (diameter of 8 μ without the processes, 10 with them).
I class under the same name, at least provisionally,
the paratype of flint 102 (5 in fig. 3) which differs from the previous one by its much longer processes (3 to 4 μ instead of 2), and especially by the absence of a membrane, of which, despite the general similarity in appearance, I could not find any trace in either of the two specimens observed. The diameter of this species therefore varies from 7 to 12 μ without the processes and from 10 to 16 μ with them.
Forms similar to the holotype are frequent in Bajocian flints from Flée (Vienne), Croisilles (Calvados); paratypes similar to 2, 3, 4, 5 in fig. 3 are rarer. The absolute identity of certain individuals from Poitou and Normandy may lead one to hope that this would be a characteristic species, and this all the more so since no similar form has been described in the Cretaceous. In the Silurian, we know a species, Micrhystridium pavimentum Defl., similarly decorated with processes connected by membranes, but which is very different from Micrhystridium eupeplos; the processes are more numerous, shorter, the fields smaller and, moreover, the dimensions are more than double.
Holotype: Bajocian, Croisilles flint (Calvados).
Paratypes: Bajocian, Croisilles flint (Calvados); Bathonian, Lessart flint (Vienne) (flint no. 98); Bathonian, Lessart flint (Vienne) (flint no. 102).
A membrane surrounds the shell, of a regularly spherical shape, attaches to the ends of the processes and draws polygonal fields on the upper face; the processes, about fifteen in number, have the shape of a T with very elongated branches on which this membrane rests. The holotype specimen (1 in fig. 3) has a diameter of 10 μ without the processes and 14 μ including them.
All the individuals observed have a dark brown color.
The paralype of flint 98 (Balhonian of Lessart) (2, 3 of fig. 3)
shows much more numerous processes (about 25), very clear and very regular polygonal fields on the angles of which are inserted the processes, in the form of short, straight and hollow rods, the diameter is 12 μ without the processes and 16 μ with them; the same type is represented in a flint from the Bajocian of Croisilles by a smaller form (diameter of 8 μ without the processes, 10 with them).
I class under the same name, at least provisionally,
the paratype of flint 102 (5 in fig. 3) which differs from the previous one by its much longer processes (3 to 4 μ instead of 2), and especially by the absence of a membrane, of which, despite the general similarity in appearance, I could not find any trace in either of the two specimens observed. The diameter of this species therefore varies from 7 to 12 μ without the processes and from 10 to 16 μ with them.
Forms similar to the holotype are frequent in Bajocian flints from Flée (Vienne), Croisilles (Calvados); paratypes similar to 2, 3, 4, 5 in fig. 3 are rarer. The absolute identity of certain individuals from Poitou and Normandy may lead one to hope that this would be a characteristic species, and this all the more so since no similar form has been described in the Cretaceous. In the Silurian, we know a species, Micrhystridium pavimentum Defl., similarly decorated with processes connected by membranes, but which is very different from Micrhystridium eupeplos; the processes are more numerous, shorter, the fields smaller and, moreover, the dimensions are more than double.