Helicocyclus Schindewolf, 1951

Korn, Dieter, Bockwinkel, Jürgen, Ebbighausen, Volker & Klug, Christian, 2003, Palaeobiogeographic and evolutionary meaning of an early Late Tournaisian ammonoid fauna from the Tafilalt of Morocco, Acta Palaeontologica Polonica 48 (1), pp. 71-92 : 84-85

publication ID	https://doi.org/ 10.5281/zenodo.13272527
persistent identifier	https://treatment.plazi.org/id/03BE87DE-5A7D-FFC9-FCF8-FA8C7344FB0D
treatment provided by	Felipe
scientific name	Helicocyclus Schindewolf, 1951
status

Treatment

Helicocyclus Schindewolf, 1951 View in CoL

Type species: Pericyclus (Helicocyclus) gracillimus Schindewolf, 1951 .

Helicocyclus fuscus sp. nov.

Figs. 23C, D, 24 View Fig .

Derivation of name: After fuscus (Lat. dark−brown), because of the colour of the material.

Holotype: Specimen MB.C.3985 (coll. Bockwinkel and Ebbighausen), Fig. 23C.

Type locality and horizon: Taouz, Jebel Ouaoufilal, locality B east of Ksar Bouhamed (Tafilalt, Morocco); Oued Znaïgui Formation, early Late Tournaisian.

KORN ET AL.— TOURNAISIAN AMMONOID FAUNA FROM MOROCCO 85

C1 C2 B1 B2 A1 A2 D1 D2 F1 E1 E2 G1 F2 G2 H1 H 2

Material.— 4 specimens between 4 and 8 mm diameter.

Diagnosis.— Helicocyclus with discoidal conch at 8 mm diameter (ww/dm 0.45). Umbilicus wide (uw/dm 0.45). Umbilical margin rounded. Conch smooth. Steinkerns with three deep protractive constrictions per volution. Suture line with symmetric, lanceolate adventive lobe and V−shaped lateral lobe.

Description.—The small evolute conchs have a depressed whorl section with widely rounded flanks and venter. Umbilical margin indistinct. The holotype has three deep constrictions, which begin some distance from the umbilicus, are protractive over flanks and venter, where they form a broad salient.

The suture line of the holotype ( Fig. 24 View Fig ) has an external lobe with almost parallel−arranged, slightly sinuous flanks. Themediansaddlehasaheightofapproximatelyonefourthof the widely rounded ventrolateral saddle. The adventive lobe is as wide as the external lobe; it is lanceolate and symmetric.

Dimensions.—(in mm). Comparisons.— Helicocyclus fuscus sp. nov. is the stratigraphically oldest representative of the genus. It differs in its smooth conch from the species H. gracillimus Schindewolf, 1951 , H. involutus Kusina, 1977 , and H. tianshanicus ( Librovitch, 1927) , which all possess numerous riblets. H. divergens Riley, 1996 has a much wider external lobe.