Spitidiscus Kilian, 1910

Vašíček, Zdeněk, Błażejowski, Błażej, Gaździcki, Andrzej, Król, Maria, Lefeld, Jerzy, Skupien, Petr & Wierzbowski, Andrzej, 2020, Early Cretaceous ammonites and dinoflagellates from the Western Tatra Mountains, Poland, Acta Palaeontologica Polonica 65 (4), pp. 799-810 : 802-803

Genus Spitidiscus Kilian, 1910

Type species: Ammonites rotula Sowerby, 1827; Speeton, UK, Hauterivian, by original designation .

Spitidiscus cf. cankovi Vašíček and Michalík, 1986 Fig. 3F .

Material.—A small fragment of whorl of outer mould ( ZPAL Am. 25/9), from Cretaceous, Tatra Mountains, Poland.

Description.—Only three slight constrictions at approximately ¼ of whorl are preserved with ribs of unequal length appearing in between them. In a single complete interval between two constrictions, 8 ribs are developed on the specimen perimeter. The ribs prolong through venter without interruption. In the interval stated, a complete simple rib occurs on front side of the first constriction. Behind the constriction, a short inserted rib appears on its outside and in front of it, another shorter one ending approximately at half­whorl can be found. A set of three ribs follows: the posterior rib is complete, starting in markedly elevated, not particularly large umbilical tubercle. Another rib runs in this tubercle and starts bifurcating. A pair of bifurcated ribs lies closer to another one than the interval between the individual and the bifurcated rib. Afterwards, there is a complete simple rib which might be connected to the above­mentioned umbilical tubercle or perhaps is independent. It is followed by a shorter inserted rib reaching approximately the mid­high whorl and by the last complete simple rib. On the rear side, the rib is limited by constriction. Four ribs reach as far as the umbilicus. The height of whorl is approximately 18 mm.

Remarks.—The incomplete specimen does not allow for an unambiguous identification. Remarkable is a large number of constrictions per whorl. Bulgarian specimens which Vašíček and Michalík (1986) included in the synonymy of Spitidiscus cankovi occur in the Lower Hauterivian. Vašíček and Michalík (1986) refer it to a similar age in the Mráznica Formation, the Butkov Quarry. Avram (1995) mentions it from the Valanginian–Hauterivian boundary in Romania.

Figures

Fig. 3. The Lower Cretaceous ammonites from the Kościeliska Marl Formation in the Lejowa Valley, Tatra Mountains, Poland. A, C–E. Criosarasinella cf. subheterocostata Reboulet, 1996. A. ZPAL Am. 25/19. C. ZPAL Am. 25/7. D. ZPAL Am. 25/17. E. ZPAL Am. 25/14. B. Calcite valve of aptychus Didayilamellaptychus seranonis (Coquand, 1841), ZPAL Am. 25/12. F. Spitidiscus cf. cankovi Vašíček and Michalík, 1986, ZPAL Am. 25/9. G. Olcostephanus densicostatus (Wegner, 1909), ZPAL Am. 25/4.All in lateral view.