Genus Schwageriniformis Bensh, 1996
Subgenus Schwageriniformis
Bensh, 1996
Schwageriniformis (Schwageriniformis) acutatus
Leven, n. sp.
Plate 1, figs 23, 25, 27, 28
Etymology.
[45] Acutatus - acutate (Lat.).
Holotype.
[46] GIN 4781/20. Axial section; Iran, Anarak, Zaladou Formation,
Sample AC-25; Late Carboniferous (Pennsylvanian), Gzhelian.
Material.
[47] 9 axial and subaxial sections.
Description.
[48] Shell moderate in size, slender fusiform, with straight to
slightly convex lateral slopes and acutely pointed poles. Mature shells have 7 to 8 whorls
and measure 3.5 mm to 4.8 mm in length and 1.3 mm to 1.6 mm in diameter; form ratio 2.7 to 3.
First 3 to 4 whorls make up tightly coiled juvenarium, which is followed by loosely coiled
adult stage. Thin in inner 4 to 5 volutions and thick in following ones spirothesa composed
of tectum and thin alveolar keriotheca, its thickness in last whorl 0.06 mm to 0.07 mm.
Septa essentially plane across middle of shell, becoming moderately fluted near poles.
Proloculus small, its outside diameter 0.04 mm to 0.05 mm. Tunnel about half as high as
chambers, narrow in the juvenarium, significantly widening outwards. Low and narrow
chomata developed in early 4 to 5.5 volutions.
Discussion.
[49] Schwageriniformis acutatus n. sp. is very similar to
Schwageriniformis schwageriniformis (Rauser-Chernousova) characteristic of the upper
zone of the Kasimovian and, to a lesser degree, of the lower zone of the Gzhelian in a great
deal of sections of the East European Platform, Urals, and Central Asia. The Iranian species
differs in a stronger isolated juvenarium and smaller chomata. The forms
similar to Schwageriniformis acutatus were recorded by V. I. Davydov in the uppermost Gzhelian of the
Darvaz region and Chios Island, Greece (personal communication). However, they
possess a greater number of whorls and greater size, which indicates their relatively
advanced character.
Occurrence and age.
[50] The same as holotype.
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