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Species / Dicroloma Nudispira


Original diagnosis:

  • Obtuse conical protoconch consisting of 2.5 smooth whorls. Teleoconch beginning with two blunt spiral keels and opisthocline axial ribs restricted to area somewhat above and beneath upper keel. On second whorl of teleoconch, upper keel composed of four subordinate spiral ribs, axial ribs restricted to surface of keel only. Lower keel much weaker, ornamented with weak axial ribs. During ontogeny, lower keel and axial ribs get weaker, and finally disappear. Surface of later whorls smooth.

Original Description of Dicroloma nudispira by Kaim, 2004:

  • Protoconch 1 is not ornamented. The transition from the protoconch to the teleoconch has an intermediate zone that is ornamented with opisthocyrt growth lines and small pustules. The adult shell peristome is not known.

Locus typicus: Faustianka, Częstochowa region, Poland

Stratum typicum: Procerites progracilis zone, mid Bathonian, Jurassic

Measurements: Protoconch 1 (holotype) consisting of one whorl is 0.19 mm. The protoconch (ZPAL (Institute of Paleobiology, Polish Academy of Sciences in Warsaw ) Ga.9/40) with 2.5 of the whorl is 0.77 mm in diameter and 0.72 mm high. The largest shell studied consists of 7.5 whorls and is 3.78 mm in diameter and 6.00 mm high.

Original remark of Kaim, 2004:

  • The species is similar to Dicroloma cochleata but it differs from it in having stronger axial ribs on the first two whorls of the teleoconch while the later whorls are smooth.

Dicroloma nudispira Kaim, 2004; mid Bathonian, Jurassic; Faustianka, Częstochowa region, Poland

  • upper row; left ZPAL Ga.9/39; second and fourth. ZPAL Ga.9/41 (holotype); third Ga.9/38
  • lower row; left Ga.9/38; second and third ZPAL Ga.9/41 (holotype); fourth ZPAL Ga.9/40; white arrow indicates demarcation between protoconch and teleoconch.

Copyright Polish Academy of Sciences & A. Kaim


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