Planiturbo lerensis, Szabó & Jaitly, 2019

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 : 10-11

Planiturbo lerensis n. sp.

( Figs 17–28 )

Type specimens – Holotype Inv. No.: BHU 2020I 4; paratype Inv. No.: BHU-2020I 5.

Type locality – Near Ler , Kachchh, western India .

Type strata – Upper Chari Formation , Callovian .

Derivation of name – From the name of village Ler.

Diagnosis – Shells of about five dextral whorls, initial ones discoidally coiled, resulting concave apex. Trochospiral coiling started from third whorl with convexly arched surface. Base slightly less convex than last whorl, transition between them widely arched. Moderately broad umbilicus with angular basal rim present. Aperture suborbicular, peristome continuous with thick parietal part. Ornament of several subequally spaced, strong, nodulose carinae, starting from third whorl. Transverse ornament of collabral riblets between pairs of carinae. Growth lines appearing like thin threads.

Material – Two multi-damaged specimens; the shell remnants are strongly fragmented on the surface of porous infilling sediment; their further cleaning would be too risky.

Measurements – Inv. No.: BHU 2020I 4; H dam. = 9.6 mm, D dam. = 10.8 mm; Inv. No.: BHU 2020I 5; H dam. = 9.3 mm, D dam. = 10.7 mm.

Description – Shells consist of 4.5 to 5 whorls; the earliest 2.5 to 3 ones are coiled in dextral discoidal way so they form broad, slightly concave apical area. In this shell region the whorls are flat and sharply angular along the abaxial suture; the suture itself is flush here. From the third whorl, the coiling gradually alters into trochospiral; the abaxial angulation becomes increasingly rounded then the whole whorl surface changes into convexly arched. The last whorl turns into the less convex base through a rather wide arch. A rather broad umbilicus with angular rim and almost cylindrical inner wall is observed in both specimens. From the peristome, only the parietal lip is preserved; it consists of a thick, smooth shell layer and a part of an inner, possibly circular, thickening along the basal edge. The shell remnants are indicative of a suborbicular aperture and a prosocline, entire peristome with wide “V”-shaped inner lip and largely arched outer lip with tubular nodules or spines as terminal processes of the carinae.

From the terminal half of the second coil, single swollen spiral belts start along both sutures, which have been formerly flush. Soon spirally elongate nodules appear on these swellings. From the third whorl, the swollen belts become nodosed carinae. Between them, subregularly repeated, sparse, feebly prosocline, collabral ribs develop. From the fourth whorl a third carina also appears halfway between the former ones then the number of carinae gradually increases to 5 or 6 for the last growth phase. In addition, four similar carinae are present also on the last base; one is just at the rim of the umbilicus. The early ribs become unequally thinner and denser from the beginning of the fourth whorl; these sharp riblets remain the transverse ornament of the succeeding whorls and the base. The growth lines are fine but sometimes as marked as thin threads, which are much weaker and denser than the riblets.

Remarks – Comparable species from Bathonian strata is published by COSSMANN (1885) as Turbo planispira (1885, p. 262, Pl. VII, figs 43–46). FISCHER, J.-C. (1969) designated it as the type species for genus Planiturbo . The specimens from Ler are similar to the type species but the differences support their new species status: the early, markedly ribbed whorl part, following the planispiral portion, is lacking from the type species just like the thin riblets on the subsequent whorls and the base of Planiturbo lerensis n. sp. The nodules of P. lerensis n. sp. are much smaller on the base than in P. planispira and this seems to be true also for the nodes of the whorls that are poorly preserved.

Occurrence – Ler, upper Chari Formation, Callovian.

Figures

Figs 17–30. Species of Vetigastropoda, and Neritimorpha.– Figs 17–23. Planiturbo lerensis n. sp., holotype. – 17–20. Apertural, apical, basal, and abapertural views, ×2.8. – 21. Details of the early shell, ×9. – 22. Details of the basal ornament, ×7.6. – 23. Details of the last whorl ornament, ×7. – Figs 24–28. Planiturbo lerensis n. sp., paratype. – 24–27. Abapertural, apertural, basal, and apical views, ×2.8. – 28. Details of the earliest whorls, ×10.3. – Figs 29–30. Colubrellopsis? sp., abaper- tural, and apical views, ×7.3