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Figure 9. Sketch of Turritella jhuraiensis Mitra and Ghosh, 1979. (1) Diagram showing all the primary spirals present in the adult whorls (maximum diameter 9.3 mm); (2) diagram showing all the primary spirals and one secondary spiral present within the A and B spiral (maximum diameter 6.2mm); (3) diagram showing the growth line patterns of the species, i.e., straight and faint prosocline (maximum diameter 3.9 mm).
primary spirals are equal, but in T. jhuraensis, spirals B and C are closer than spirals B and A. Moreover, number of secondary spirals is greater in T. jadavpuriensis, while in T. jhuraensis only a single faint secondary spiral is present. These two species also differ in their growth lines. Turritella jadavpuriensis is characterized by a curved, prosocline lateral growth line (growth line formula is 3-3-M-A/C-P), while it is straight (albeit faint) in T. jhuraensis. Turritella jadavpuriensis is basally bicarinate, while T. jhuraensis has three basal cords; the middle one is weakly developed. The aperture in T. jadavpuriensis is subquadrate, while in T. jhuraensis it is subrounded. Turritella jhuraensis resembles T. pelusae, described byVon
der Osten (1957, p. 586, pl. 65, fig. 15) from the Lower Cretaceous of Venezuela, in having similar shell size and whorl profile. Turritella jhuraensis, however, differs from the South American species in having a higher apical angle (22–26° versus 13° in T. pelusae). Von der Osten mentioned the presence of five ribs on early whorls and one additional rib on later whorls, but he did not specify which spiral he was referring to. In contrast, T. jhuraensis has three primary spirals and two secondaries up to the last whorls, and these and spiral elements have varying strength, whereas in Venezuelan species they are of equal strength.
Figure 10. (1–3) Turritella jhuraensis Mitra and Ghosh, 1979. (1, 2) Apertural and abapertural views (paraneotype no. ISI/g/Jur/T 32). Specimens are coated with magnesium oxide; (3) SEM image of early teleoconch whorls of the same species (paraneotype no. ISI/g/Jur/T 33) showing three primary spirals of varying strength (see systematic description for details). Scale bars = 1 cm; (4–6) Turritella amitava new species. (4, 5) Apertural and abapertural views (paratype no. ISI/g/Jur/T 45). Specimen is coated with magnesium oxide; (6) SEM image of early teleoconch whorls of the same species (paratype no. ISI/g/Jur/T 46) showing three spirals of equal strength (see systematic description for details). Scale bars = 1 cm.
toulmini described by Allmon (1996, p. 90, pl. 12, figs. 6, 7) from the lower Paleocene Clayton Formation of Alabama in having a similarly convex whorl profile. Turritella jhuraensis, however, differs from the American species in having a smaller and less slender shell (apical angle in T. toulmini 10° versus 22–26° in T. jhuraensis). Although both species have same number of spiral threads, the strength of spirals in T. toulmini is about equal. In T. jhuraensis they are of varying strength. Turritella jhuraensis is very similar to T. narica, described
Turritella jhuraensis is also comparable to “Turritella”
from the Miocene Khari Nadi Formation of Kutch (Vredenburg, 1928, p. 375, pl. 18, figs. 13–17, 21, pl. 19, figs. 2, 6; Kulkarni et al., 2010, p. 312, fig. 2d, e) in having a similar apical angle and whorl profile. But T. narica is larger (maximum observed height 37.0mm compared to 28.2mm in
T. jhuraensis). Moreover, sculpture in T. jhuraensis consists of five spiral threads of unequal strength while T. narica has six spirals, of which five are of equal strength and the basal thread is stronger.
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