Diatrypesis sp. 2

Diatrypesis sp. 2

( Figs 37–40 View Figs 31–59 )

Material – Two fragmentary and worn specimens of 5–5 whorls without earliest and latest shell parts.

Measurements – Inv. No.: BHU 2020I 10; H dam. = 10.7 mm, D dam. = 5.3 mm, pleural angle: 22°; Inv. No.: BHU 2020I 11; H dam. = 9.5mm, D dam. = 4.6 mm, pleural angle: 22°.

Description – With their partly preserved base, both specimens seem to represent latest growth phase of a species, having turriculate shell of conoidal outline. The whorls are almost flush but a shallow concave zone follows the subsutural carina that shifts into low convex surface in abapical half of the whorl; the convexity continues towards the base on the last whorl. The suture is sharply impressed.

The subsutural carina bears rather marked nodes; dense, very fine spiral threads complete the spiral ornament. Dense, thin, collabral riblets cover the early preserved whorls; they gradually vanish during the growth and lack from the latest whorls. The growth lines and the riblets are markedly opisthocline, and opisthocyrt. The abapical part of the growth lines approaches the direction of the spiral lines in the peripheral/outer base area.

Remarks – The coiling angle does not differ significantly from that measured in Diatrypesis sp. 1 , but the whorls are slightly lower and less convex; they are also ribbed in early growth phases then the ribs disappear and the nodules of the subsutural carina persist also on the whorls without ribs. However, the ribs, as well as the growth lines, are more opisthocline and more opisthocyrt than in Diatrypesis sp. 1 .

Diatrypesis sp. 2 seems closely related to that one, which represents Diatrypesis sp. 1 . They may belong to a single evolutionary lineage or just to a single species of unknown (high) variability.

Occurrence – Keera Dome, Chari Formation, Callovian.