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Journal of Paleontology 92(3):373–387
Sowerby, 1840 (see Harzhauser et al., 2009, p. 341, fig. 3j–n), strongly resembles T. jhuraensis in many characters, including shell size, shell outline, whorl profile (flat to convex), and moderately impressed suture. Harzhauser et al. (2009) provide a detailed account of the ontogeny of spiral sculpture in T. assimilis. In both species, the early teleoconch whorls possess three primary spirals, but in T. assimilis many secondaries develop later. One of them, located near the anterior suture, becomes equal in strength with the primaries. Two additional secondaries occur between the anterior-most primary spiral and the anterior suture, and the posterior-most primary spiral and the posterior suture. Such development of secondaries is not observed in T. jhuraensis, where the total number of spiral elements including secondaries remains the same (five) all through the later part of the teleoconch.
Another Miocene species from Kutch, Turritella assimilis Turritella amitava new species Figures 10.4–10.6, 11.1, 11.2, 12.1, 12.2 Holotype.—Holotype: specimen no. ISI/g/Jur/T 41.
Diagnosis.—Shell small, with subquadrate whorls; primary teleoconch spirals equidistant; spiral B weak to obsolete; sec- ondary spirals faint and discontinuous; growth line formula 4-4- S-P.
Occurrence.—This species is known only from the Oxfordian horizons near a pond ∼1 km south-east of the village of Jhura, Kutch (23°24’47.57”N, 69°36’09.26”E).
Description.—Shells small to medium in size with nine to ten whorls. Maximum observed whorl diameter 13.5mm; max- imum observed height 28.0mm. Apical angle 20–24°; apical and pleural angles equal. Sutures weakly to moderately incised. Protoconch unknown. Apical sculpture formula C1B2A3. C spiral in earliest teleoconch in lower 1/3 of whorl; B spiral in
middle of that whorl. A spiral within upper 1/3 of third teleoconch whorl. A and C spirals in later whorls become more conspicuous, but B spiral remains relatively weak. Three primary spirals equidistant. Spiral A and spiral B separated by one secondary spiral that is weaker in strength compared to primary spiral. Spiral C and anterior suture also separated by one secondary spiral, which is very faint, discontinuous, and only preserved in two consecutive whorls at whorl diameter 6.13mm(Fig. 12). Shell basally bicarinate and carinae restricted in peripheral outer part of the base. Upper carina stronger than lower carina. Whorl profiles subquadrate to slightly concave. Lateral aspect of growth line traces slightly prosocline, straight (Fig. 12). Basal sinus shallow. Growth line formula 4-4-S-P (Allmon, 1996, text-fig. 10). Aperture axially ovate. Columellar lip distinct, outer lip very thin and fragile, in most specimens not preserved.
Etymology.—The species is named in honor of the late Amitava Koyal, Geologist, Oil and Natural Gas Corporation Limited (ONGC), India.
Materials.—Holotype (ISI/g/Jur/T 41) and 10 paratypes speci- mens ISI/g/Jur/T 42-51.
Remarks.—Turritella amitava n. sp. is comparable to the American upper Eocene species Haustator perdita (Conrad, 1865), as described by Allmon (1996, p. 74, pl. 8, figs. 1–9). Both species are small to medium size, with moderately incised sutures, and similar maximum observed whorl diameter and whorl profile. The American species, however, is more slender and has more whorls. Apical ontogeny is similar in both species, but strength and relative position of primary spirals differ. Turritella amitava n. sp. is characterized by the presence of faint and discontinuous secondary spirals, whereas H. perdita has many fine secondaries developed in different growth stages.
Figure 11. SEM image of apex of Turritella amitava n. sp. (1) Paratype (no. ISI/g/Jur/T 42) showing development of early teleoconch stage and well- developed apical sculpture (×105); (2) sketch of 1, showing primary spiral ribs (notation after Allmon, 1996). Note order of appearance of spiral ribs in ontogeny: C spiral rib appears first, quickly followed by spiral rib B, with A coming later. Therefore, apical sculpture formula is C1B2A3.
Figure 12. Sketches of late teleoconch of Turritella amitava n. sp. (1) Showing the growth line pattern, slightly prosocline and straight (maximum diameter 6.1 mm); (2) showing the spiral ornamentation, which illustrated three primary spiral ribs (A, B, C) and one secondary spiral present between spiral C and the anterior suture (maximum diameter 5.28 mm).
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