שמור ב:
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| פורמט: | Recurso digital |
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Zenodo
2022
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| גישה מקוונת: | https://doi.org/10.5281/zenodo.6302064 |
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תוכן הענינים:
- <p><b><i>Planetoceras destrictum</i> sp. nov.</b></p><p>urn:lsid:zoobank.org:act: 42BD8B9E-A638-4C4F-9472-0B0EE6AB489E</p><p>Figs 12–13; Table 8</p><p><b>Diagnosis</b></p><p>Species of <i>Planetoceras</i> with moderately depressed, rounded-pentagonal whorl profile (ww/wh ~ 1.65), venter slightly flattened, ventrolateral shoulder broadly rounded. Umbilical margin subangular to narrowly rounded, umbilical wall steep, flattened. Whorls slightly embracing.</p><p><b>Etymology</b></p><p>After the Latin ‘ <i>destrictum</i> ’, meaning ‘sharp’ and referring to the angular umbilical margin.</p><p><b>Type material</b></p><p><b>Holotype</b> ALGERIA • Gourara, Sebkha de Timimoun 14.5 km west-southwest of Timimoun; “Dalle à <i>Merocanites</i> ” (Tournaisian-Viséan boundary interval); illustrated in Fig. 12; MB.C.30385.</p><p><b>Description</b></p><p>Specimen MB.C.30385 is a fully chambered specimen with a diameter of 67 mm (Fig. 12). It is a stout, subinvolute conch (ww/dm = 0.76; uw/dm = 0.29) and has a depressed, subtrapezoidal whorl profile with a broadly rounded venter, a rounded ventrolateral shoulder, weakly flattened, slightly converging flanks,</p><p>a rounded umbilical margin and a rounded umbilical wall. It has a very high coiling rate (WER = 2.59). The specimen shows a morphological change in the shape of the umbilicus. During the last volution of the phragmocone, the umbilical margin changes from subangular to rounded. At the same time, the umbilical wall changes from flattened to rounded. The suture line extends nearly linearly across the venter and possesses a very shallow lobe on the flank (Fig. 13).</p><p><b>Remarks</b></p><p><i>Planetoceras destrictum</i> sp. nov. differs from the species described from Belgium, the South Urals and North America in the flattened venter, which is rounded in those species. More similar is <i>P. globatum</i> (Sowerby, 1824), a species with a very similar whorl profile (Histon 1999) but a more slender conch (ww/dm ~ 0.55 at 58 mm dm) than <i>P. destrictum</i> sp. nov. (ww/dm <i>~</i> 0.76 at 67 mm dm). <i>Planetoceras transforme</i> sp. nov. (described below) has a much stouter conch (ww/dm ~ 0.85).</p>