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Trilemma polivnense
Taxonomy
Trilemma polivnense was named by Blagovetshenskiy and Shumilkin (2012) [= ?Aporrhais (Tessarolax) bicarinata: Wollemann, 1912, p. 181, pl. 13, fig. 12.
= Trilemma striatocarinatum: Blagovetshenskiy and Shumilkin 2006, p. 40, pl. 6, figs. 2–6.]. Its type specimen is VDChO 220/3, a shell, and it is a 3D body fossil. Its type locality is UPM, no. 168/1-3. Polivna, which is in a Hauterivian carbonate claystone in the Russian Federation.
Synonymy list
| Year | Name and author |
|---|---|
| 2012 | Trilemma polivnense Blagovetshenskiy and Shumilkin pp. 346 - 348 figs. Plate 1, figs. 1 and 2 |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
†Trilemma polivnense Blagovetshenskiy and Shumilkin 2012
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| I. V. Blagovetshenskiy and I. V. Shumilkin 2012 | The shell is medium sized, up to 25 mm high, spindleshaped, with a wing shaped expansion of the palatal margin of the aper ure, consists of seven or eight bicarinate whorls. At the base of the last whorl of adults, under the second carina, there is a somewhat smaller third carina.
The protoconch is smooth, consists of 3.5 whorls; then, spiral ribs gradually appear and, somewhat later, axial ribs are developed. On the fourth whorl of the spire, four spiral ribs are distinct; the second upper most rib is slightly larger than others; in the fifth whorl, it becomes the first carina. In the fifth or sixth whorl, as a result of strengthening of the fourth (or, less fre quently, fifth) uppermost spiral rib, the second carina is formed. In the last whorl of adults, because of strengthened sixth or seventh uppermost rib, the weakest third carina is developed. Between the carinae, above and below them, unstrengthened spiral ribs are retained. Above the first carina of young individuals (having five whorls), there is one spiral rib (in adults, three spiral ribs, two of which are secondary). Between the first and second carinae (in the fifth or sixth whorl), a weak spiral rib is retained. In later whorls, additional (secondary) ribs (up to two in number) appear here. In the last whorl (seventh or eighth), between the second and third car inae, one or two weak spiral ribs are distinct; under the third carina, there are seven spiral ribs. The axial sculpture of the fourth whorl is composed of opistho cyrt ribs. It remains the same to the fifth whorl inclu sive and, then, becomes almost indiscernible. One whorl retains from 48 to 54 axial ribs. When crossing the axial and spiral ribs, cells in the shape narrow par allelograms, extending along the shell axis are formed. The aperture is elongated elliptical. The upper palatoparietal margin of the aperture passes into the posterior process; in adults, it extends above the initial whorls of the shell (terminology is considered in the study of Blagovetshenskiy and Shumilkin, 2006). The palatal margin of the aperture is expanded wing shaped and has two sabershaped carinate processes. The posterior lateral process, which continues the first carina, is directed horizontally posteriorly and to the right at an angle of 17°–37° (end of the process) to the whorl axis; in some individuals, it rises above the initial whorls. The anterior lateral process, which continues the second carina is directed anteriorly and to the right. The anterior process is elongated, sometimes posteriorly curved. On the inner side, the processes have grooves, which correspond to the carinae on the opposite side. |
Measurements
No measurements are available
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| Source: f = family, c = class | |||||
| Reference: Kiessling 2004 | |||||
Age range: Hauterivian or 132.60000 to 125.77000 Ma
Collections: one only
| Time interval | Ma | Country or state | Original ID and collection number |
|---|---|---|---|
| Hauterivian | Russian Federation | Trilemma striatocarinatum (type locality: 177875) |