Diatrypesis sp. 1

Diatrypesis sp. 1

( Fig. 36 View Figs 31–59 )

Material – Single, incomplete specimen is available, partly embedded on rock surface. Protoconch and latest whorl(s) are lacking.

Measurements – Inv. No.: BHU 2020I 9; H dam. = 20.3 mm, D dam. = 5.3 mm, pleural angle: 20°.

Description – Shell is rather highly turriculated; ten whorls with impressed suture represent this species. Surface of the whorls has a profile that is characteristic for the teleoconch of Diatrypesis : a marked carina just below the suture, accompanied by a shallow concavity abapically, and a wider, convex area below it. The convex area forms also the periphery of the whorls; the latest whorl smoothly turns into the base. The broken surface of the last whorl shows cross-section of a siphonal outlet in its axial area.

The early whorls are collabrally ribbed between the lower suture and the subsutural carina that is sparsely nodosed. The ribs gradually shorten and weaken during the growth but the nodulae of the carina persist along the entire shell. Dense, fine threads mean the spiral ornament on the visible whorls.

The growth lines and the ribs are opisthocline, and slightly opisthocyrt in the abapical half of the early whorls; the opisthocyrt form almost fully disappears for the latest whorls.

Remarks – Diatrypesis sp. 1 differs from most of the formerly published species in its less markedly ornamented nature. Most of these species are ribbed even on the last whorls differently from Diatrypesis sp. 1 . In the unribbed latest whorls, the Bajocian Diatrypesis angulocostatum (Szabó, 1983) is similar to Diatrypesis sp. 1 , however, it has flush last whorls and the subsutural carina (cord) is without nodules but densely crossed by tiny riblets.

Occurrence – Jumara Dome, Patcham Formation, Bathonian.