Das et al.—Oldest turritelline gastropods from the Upper Jurassic of India
The two species also differ in the nature of growth line patterns. Growth line formula is 4-4-S-P for T. amitava n. sp., compared to 4-2-M-B/C-P/OR for H. perdita.
Turritella dhosaensis new species Figures 13.1, 13.2, 14.1–14.5
Holotype.—Specimen no. ISI/g/Jur/T 52.
Occurrence.—This species is known only from the Oxfordian horizons ~ 1km south-east of the village of Jhura near a pond, Kutch (23°24’47.57”N, 69°36’09.26”E).
Description.—Shell small to medium in size with eight to nine preserved whorls. Maximum observed whorl diameter 7.5mm; maximum observed height 23.2mm. Pleural angle 22°. Suture deeply grooved. Protoconch and early teleoconch whorls unknown. Earliest known whorl ~ 2.0mm in diameter. A, B, and C spirals prominent; strength of spirals decreases from posterior suture to anterior suture. Primary spiral A remains strong throughout ontogeny. Space between A and B spirals wider than space between B and C. No secondary spirals between primary spirals (Fig. 13). Shell basally bicarinate, carina thin and sharp at its peripheral (outer) margin. Whorl profiles telescoped. Lateral aspect of growth line traces indis- tinct, slightly prosocline, convex with inflection point at or above mid-whorl. Basal aspect of growth line traces not dis- cernible (Fig. 13). Aperture axially ovate. Columellar lip dis- tinct, outer lip thin.
Etymology.—The species is named after the Dhosa Oolite Member of the Chari Formation in which it is found.
Materials.—Holotype (ISI/g/Jur/T 52) and 13 paratype speci- mens ISI/g/Jur/T 53-65.
383
Remarks.—Turritella dhosaensis n. sp. has a telescoped whorl profile, whereas whorl profiles are subquadrate to slightly con- cave in T. amitava n. sp., described above. In T. amitava n. sp., the distances among primary spirals are equal, but in T. dhosaensis n. sp., spirals BandCare closer than spiralsAand B. Moreover, T. dhosaensis n. sp. lacks secondary spirals, while in T. amitava n. sp., a number of secondary spirals are present. Turritella dhosaensis n. sp. is characterized by indistinct, slightly prosocline, convex lateral growth lines with the inflection point at or above the mid-whorl, while it is slightly prosocline or straight in T. amitava n. sp. Turritella dhosaensis n. sp. resembles Haustator tennes- seensis (Gabb, 1860) of the lower Paleocene of the Gulf and
Atlantic coastal plains, USA (Allmon, 1996, p. 79, pl. 7, figs. 6–9) in having a similar shell size, number of primary spirals (three), growth line pattern (both have slightly prosocline growth line traces), and absence of secondary spirals. However, the American species has more whorls. Both species also differ in their whorl profiles: H. tennesseensis is characterized by trapezoidal to concave whorl profiles, while it is telescoped in T. dhosaensis n. sp. Turritella dhosaensis n. sp. is similar to another American
species, Haustator rina (Palmer, 1937), described by Allmon (1996, p. 76, pl. 10, figs. 1, 4, 5) from the middle Eocene Lisbon Formation. Both species have similar number of primary spirals, suture (deeply incised), and growth line patterns (slightly prosocline growth line traces and inflection points above the mid-whorl). Haustator rina, however, is characterized by mediumto large shell, straight-sided whorl profile, and presence of faint secondaries while T. dhosaensis is characterized by small- to medium-sized shell, telescoped whorl profiles and lack of secondaries. Another American upper Eocene species, Haustator
perdita (Conrad, 1865), described by Allmon (1996, p. 74, pl. 8, figs. 1–9), is also similar to the new species. Both species have similar shell size and similar number of primary spirals. The American species, however, has more whorls. Secondary spirals are present between primaries in H. perdita, while it is absent in T. dhosaensis n sp. Whorl profile and growth line patterns, however, also differ. In H. perdita, the whorl profile is subquadrate, while it is telescoped in T. dhosaensis n. sp. Lateral growth line traces is orthocline to slightly prosocline in H. perdita, whereas it is slightly prosocline in T. dhosaensis n. sp. Turritella dhosaensis n. sp. can be compared with Incatella
Figure 13. Sketches of adult whorl of Turritella dhosaensis n. sp. (1) Showing the spiral ornamentation that demonstrates three primary spiral ribs (A, B, C) throughout the late growth stage (maximum diameter 7.5 mm). Note the absence of secondary spiral within the primaries; (2) growth line patterns, slightly prosocline, convex with inflection point at or above the mid-whorl (maximum diameter 7.5mm).
cingulatiformis Möricke in Möricke and Steinmann, 1896 from the Oligocene to Miocene of southern Peru (DeVries, 2007, p. 334, fig. 3.4–3.7, 3.20) in having similar number of primary spirals (three). Incatella cingulatiformis, however, has a number of secondary spirals, while they are absent in T. dhosaensis n. sp. Moreover, the Peruvian species attains a very large size (up to 70mm) and has more whorls and a more acute pleural angle. These two species also differ in their whorl profiles and growth line traces. Incatella cingulatiformis is characterized by strongly subquadrate whorls and the growth line formula is 1/2-1-M-A- OR/OP, while T. dhosaensis n. sp. is characterized by telescoped whorl profiles and an indistinct, convex and slightly prosocline lateral growth line. Another Cenozoic species from western Pacific Islands (Pliocene and Pleistocene), Turritella (Kurosioia) fileola
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