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Micrhystridium polyedricum
Original description: [Valensi, 1949, p. 548-549] (translated from French):
Micrhystridium polyedricum nov. sp.
Fig. 6.
Holotype: Bajocian, flint from the Porteau rock in Poitiers.
Paratypes: Bathonian, flint from the Tour aux Cognons (Vienne),
flint from Lessart (Vienne); Aalenian, flint from the Gouex quarry (Vienne).
This species is always easily recognizable by its rectangular shell, the short sides of which are surrounded by a crown of processes.
In the holotype (1 of fig. 6), the processes are all quite short, spine-shaped and very widened at the base, except for one which is much
longer. The long sides are straight and parallel, while the short sides are rounded and surrounded by a crown of four processes at one end and five at the other. The long side of the shell measures 8 μ, the short side 6 μ, the greatest distance between the two short sides, that is to say that from one bulge to the other, is 9 μ. The long process measures 4 μ, the others 2 μ. All specimens of this species have a dark brown color and
generally present an accentuated relief.
The numerous paratypes and individuals observed (1 to 13 in fig. 6) show quite notable variations affecting both the shell and
the processes. The shell can narrow towards one of its ends and thus take a slightly trapezoidal shape (3 and 6 in fig. 6); a process may appear in the middle of a long side, but I have never observed one on both long sides at the same time, often (8 and 12 in fig. 6) we find only 3 processes around one of the short sides and 2 around the other, a longitudinal rib may cross the shell (13 in fig. 6) parallel to the long side and connect two processes.
The processes are sometimes short and widened at the base (9 in fig. 6) where the processes are 2 μ long by 1 wide at their birth and
reduced to a wart (11 in fig. 6), sometimes 4 μ long (12 in fig. 6) and even 6 μ (13 in fig. 6); they can be straight or curved at their
end. The different figures will give better than a long description a rapid and exact idea of the variations of this species.
This species, already present in the Aalenian, is common in the Bajocian and Bathonian of the Poitiers region; it is rare: only 1 specimen with long processes in the flints of the Airvault region, and has not been found so far in Norman flints. No similar species has yet been described in the Silurian or the Cretaceous.
Micrhystridium polyedricum nov. sp.
Fig. 6.
Holotype: Bajocian, flint from the Porteau rock in Poitiers.
Paratypes: Bathonian, flint from the Tour aux Cognons (Vienne),
flint from Lessart (Vienne); Aalenian, flint from the Gouex quarry (Vienne).
This species is always easily recognizable by its rectangular shell, the short sides of which are surrounded by a crown of processes.
In the holotype (1 of fig. 6), the processes are all quite short, spine-shaped and very widened at the base, except for one which is much
longer. The long sides are straight and parallel, while the short sides are rounded and surrounded by a crown of four processes at one end and five at the other. The long side of the shell measures 8 μ, the short side 6 μ, the greatest distance between the two short sides, that is to say that from one bulge to the other, is 9 μ. The long process measures 4 μ, the others 2 μ. All specimens of this species have a dark brown color and
generally present an accentuated relief.
The numerous paratypes and individuals observed (1 to 13 in fig. 6) show quite notable variations affecting both the shell and
the processes. The shell can narrow towards one of its ends and thus take a slightly trapezoidal shape (3 and 6 in fig. 6); a process may appear in the middle of a long side, but I have never observed one on both long sides at the same time, often (8 and 12 in fig. 6) we find only 3 processes around one of the short sides and 2 around the other, a longitudinal rib may cross the shell (13 in fig. 6) parallel to the long side and connect two processes.
The processes are sometimes short and widened at the base (9 in fig. 6) where the processes are 2 μ long by 1 wide at their birth and
reduced to a wart (11 in fig. 6), sometimes 4 μ long (12 in fig. 6) and even 6 μ (13 in fig. 6); they can be straight or curved at their
end. The different figures will give better than a long description a rapid and exact idea of the variations of this species.
This species, already present in the Aalenian, is common in the Bajocian and Bathonian of the Poitiers region; it is rare: only 1 specimen with long processes in the flints of the Airvault region, and has not been found so far in Norman flints. No similar species has yet been described in the Silurian or the Cretaceous.