Cymaclymenia subvexa, Klein & Korn, 2014

Klein, C. & Korn, D., 2014, A morphometric approach to conch ontogeny of Cymaclymenia and related genera (Ammonoidea, Late Devonian), Fossil Record 17 (1), pp. 1-32 : 13-15

Cymaclymenia subvexa n. sp.

Figures 13 and 14

1960 Cymaclymenia striata . – Petter, p. 47, pl. 7, figs. 16, 17, 19, pl. 8, figs. 1, 4, 13.

1999 Cymaclymenia cordata . – Korn, p. 170, pl. 4, fig. 5.

Derivation of name: After Lat. subvexus, -a, -um (adj.) = oblique, because of the shape of the umbilical wall.

Holotype: Specimen MB.C.22658 (Rücklin 2003 Coll.); illustrated here in Fig. 13a .

Type locality and horizon: Bou Ifarherioun 17 km south of Rissani; Gonioclymenia Assemblage (late Famennian).

Material: 383 specimens with a maximum conch diameter of 50 mm.

Diagnosis: Species of Cymaclymenia with thinly discoidal conch in the adult stage (ww / dm = 0.30–0.35); whorl cross section weakly compressed (ww / wh = 0.65). Conch shape in the intermediate stage (10 mm dm) thinly discoidal and subevolute (ww / dm = 0.32; uw / dm = 0.32). Umbilical wall oblique in the adult stage, flanks moderately converging, venter narrowly rounded. Ornament with very fine biconvex growth lines and with weak riblets on the flank.

Discussion: Cymaclymenia subvexa is one of the slender species of the genus. It differs from many of the other species in the presence of riblets on the inner flanks. Of the Uralian species, C. decorata Nikolaeva and Bogoslovsky, 2005 has even stronger and sharper riblets and C. crenata Nikolaeva and Bogoslovsky, 2005 has a rather blunt lateral lobe as well as a stronger biconvex course of the growth lines. C. silesiaca ( Renz, 1914) from Silesia possesses steinkern constrictions at the end of growth.

The new species resembles Procymaclymenia ebbighauseni and Cymaclymenia formosa in conch geometry and ontogeny. P. ebbighauseni is easily separable by the suture line (blunt in P. ebbighauseni , pointed in C. subvexa ), but the differences with C. formosa are less obvious. The two species can best be separated by the form of the umbilical wall, which is oblique in C. subvexa (with an inclination of about 45 ◦) but steep in C. formosa . C. serotina lacks the flank riblets of C. subvexa .

Figures

Figure 13. Cymaclymenia subvexa n. sp. from the Anti-Atlas of Morocco; all × 1.0. (A) Holotype MB.C.22658 (Rücklin 2003 Coll.) from Bou Ifarherioun. (B) Paratype MB.C.22636.1 (Korn 1998 Coll.) from Madène el Mrakib. (C) Paratype MB.C.22656.1 (Korn 1993 Coll.) from Bou Tchrafine. (D) Paratype MB.C.22656.2 (Korn 1993 Coll.) from Bou Tchrafine. (E) Paratype MB.C.22691.1 (Ebbighausen 1988 Coll.) from Fezzou. (F) Paratype MB.C.22691.2 (Ebbighausen 1988 Coll.) from Fezzou. (G) Paratype MB.C.22691.3 (Ebbighausen 1988 Coll.) from Fezzou. (H) Paratype MB.C.22689.1 (Ebbighausen 1988 Coll.) from Fezzou.

Figure 14. Cross sections (A–I; all × 1.5) and ontogenetic trajectories (J–M) of Cymaclymenia subvexa n. sp. from the Anti-Atlas of Morocco. (A) Paratype MB.C.22647.1 (Korn 2009 Coll.) from Madène el Mrakib. (B) Paratype MB.C.22686.1 (Wendt Coll.) from Khorb et Attil. (C) Paratype MB.C.22675 (Wendt Coll.) from Bou Ifarherioun. (D) Paratype MB.C.22636.2 (Korn 1998 Coll.) from Madène el Mrakib. (E) Paratype MB.C.22682 (Wendt Coll.) from Taourirt. (F) Paratype MB.C.22686.2 (Wendt Coll.) from Khorb et Attil. (G) Paratype MB.C.22683.1 (Wendt Coll.) from Taourirt. (H) Paratype MB.C.22684.1 (Wendt Coll.) from Taourirt. (I) Paratype MB.C.22636.3 (Korn 1998 Coll.) from Madène el Mrakib. (J) Conch width index (ww /dm). (K) Umbilical width index (ww /wh). (L) Whorl width index (uw / dm). (M) Whorl expansion rate (WER).