Diatrypesis Tomlin, 1929

Szabó, János & Jaitly, Anand Kumar, 2019, Additional Middle Jurassic gastropods from Kachchh (western India) in the collections of the Banaras Hindu University (Varanasi, India), Fragmenta Palaeontologica Hungarica 36, pp. 3-30 : 15-16

Genus Diatrypesis Tomlin, 1929

Type species – Cerithium guerrei Hebert et Deslongchamps, 1860

Diatrypesis sp. 1

( Fig. 36)

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.

Diatrypesis sp. 2

( Figs 37–40)

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.

Diatrypesis ? sp.

( Figs 41–42)

Material – Single, slightly flatten teleoconch fragment with eroded shell remnants.

Measurements – Inv.No.: BHU 2020I12; H dam.= 23.6 mm, pleural angle:~14°.

Description – Plan of the shell is similar to those of Diatrypesis sp. 1 and sp. 2 above, however, the subsutural carina is represented here by a low, ribbon like elevation without nodules. Sparse, rather strong, straight, sharp ribs cross the whorls on the earliest preserved whorl from suture to suture; on this shell part, their orientation is slightly opisthocline. On the following whorls, the ribs become orthocline and less marked.

Remarks – The differences in the morphology from the above Diatrypesis species may hold generic level taxonomic meaning; however, the state of preservation does not allow to clarify it.

Occurrence – Jumara Dome, Jhurio Formation, Bathonian.