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Genetrix petrushevskayae Sugiyama, 1994

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Genus Genetrix Sugiyama n. gen.
Type species: G. petrushevskayae Sugiyama n. sp.
Diagnosis: Test large, consisting of two segments of small cephalis and large thorax that is longer than wide. Internal spicule composed of MB, A, D, two L, V and Ax. A has three, prominent branches a that are nearly parallel to D and two L, and protrudes cephalic wall as an apical spine. D and two L incorporated with thoracic wall, forming three ribs, and further extending beyond thoracic margin as divergent feet. Branches c and p are stout, and arches cD and pL are as thick as cp and pp. V extending obliquely upward (nearly 30°-45° upward from the horizontal), and penetrating cephalic wall above arch pp. Arches ac and ap present or absent. There are three, delicate panels (Goll, 1979) outside shell wall, which extends from the distal part of the apical spine along the thoracic ribs.
Remarks: This genus resembles Clathromitra Haeckel, 1881, from which it is distinguished by having a long thorax, extensions of D and two L incorporated with thorax, and V intersecting above thick arch pp.
Range: Early Miocene so far as known.
Sugiyama 1994
Genetrix petrushevskayae
Description: Test as with genus. Cephalis pierced by a lot of subcircular pores of various size. Some specimens have arches ac and ap, but they are not traceable in others. Collar stricture is marked by a gentle change in contour. Thorax divided into barrel-shaped upper and frustum lower parts by a central constriction without internal structures. The upper thorax more or less sinuated, with the maximum width at the middle, pierced by larger, subcircular to subangular pores arranged without regularity; bars thin, oval to circular in cross section. Cephalis and the upper thorax generally covered by a spongy mantle. The lower thorax is as long as or slightly shorter than the upper part, and the margin is commonly wider than the maximum diameter of the upper part. Pores of the lower thorax commonly subangular, and bars are thin. Feet slightly curved inward and three-bladed.
Remarks: Refer to the generic remarks. The abundance is very rare to extremely rare in the examined samples.
Dimensions (in µm): Length of apical spine 35-60; of cephalis 40-60; of thorax including feet 150-250. Maximum width of the upper thorax without panels; 90-150.
Sugiyama 1994











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