Pseudoprobeloceras applanatum

Pseudoprobeloceras applanatum (Wedekind, 1918)

Figs 4B, 7

Gephyroceras Pernai var. applanata Wedekind, 1918: 122, 167, pl. 21 fig. 3, text-fig. 28b.

Ponticeras pernai applanata – Matern 1931: 80. — House in House & Ziegler 1977: 79, pl. 1 figs 16– 17, 26–27.

Pseudoprobeloceras applanatum – Korn & Klug 2002: 98.

Diagnosis

Species of Pseudoprobeloceras reaching about 50 mm conch diameter with thinly discoidal, subinvolute conch at 30 mm dm (ww/dm ~ 0.35; uw/dm ~ 0.28); coiling rate moderate (WER ~ 1.95). Whorl profile weakly compressed (ww/wh ~ 0.85); umbilical wall oblique, umbilical margin broadly rounded, venter weakly flattened, ventrolateral shoulder narrowly rounded. Growth lines very fine, strongly biconvex with linguiform ventrolateral projection. Suture line with V-shaped external lobe with diverging flanks; median saddle low, E 2 lobe small, rounded, ventrolateral saddle almost symmetrically rounded, lateral lobe asymmetrically rounded.

Material examined

Holotype GERMANY • Rhenish Mountains, Oberscheld (Grube Prinzkessel); late Givetian (Red Ironstone); Welsch 1912 Coll.; SMF.Mbg.2323. Illustrated by Wedekind (1918: pl. 21 fig.3) and House & Ziegler (1977: pl. 1 figs 26–27); re-illustrated here in Fig. 4B.

Additional material

GERMANY • 1 specimen; Rhenish Mountains, Oberscheld (Grube Volpertseiche); late Givetian (Red Ironstone); Koch Coll.; MB.C.22157.

Description

Two specimens are selected for description and illustration:

Holotype SMF.Mbg.2323: rather well-preserved specimen with 24 mm diameter in haematitic limestone (Fig. 4B).

MB.C.22157: incomplete specimen with about 44 mm diameter in haematitic limestone; more than half of the last volution belong to the body chamber (Fig. 7A).

Holotype SMF.Mbg.2323 with 24 mm diameter is discoidal and subinvolute (Fig. 4B). Its umbilical wall is rounded; the flanks slightly flattened and converge to the rather broad venter. A pronounced, weakly angular ventrolateral shoulder is present on the entire last volution. The growth lines are lamellar; there are faint riblets around the umbilicus. The suture line has a large, subdivided external lobe with very small E 1 prongs, a low median saddle and a very deep E m lobe.

Specimen MB.C.22157, 35 mm in diameter, has a thinly discoidal and subinvolute conch with a compressed whorl profile (Fig. 7A). It is widest near the mid-flank and has an oblique umbilical wall and broadly rounded umbilical margin; the flanks are convex and weakly convergent, the outer flanks are weakly concave and separated from the weakly flattened venter by a narrowly rounded ventrolateral shoulder. The shell remains show rhythmically strengthened growth lines with broadly rounded dorsolateral projection, a wide lateral sinus and a narrow and high, lingulate ventrolateral projection. The suture line is barely visible in the ventral portion because of poor preservation; it possesses a V-shaped external lobe, a narrowly rounded ventrolateral saddle and a broadly rounded lateral lobe (Fig. 7B).

Remarks

Pseudoprobeloceras applanatum differs in the slightly stouter conch shape (ww/dm ~ 0.35) from P. pernai (ww/dm = 0.20–0.30) and the narrower umbilicus (uw/dm ~ 0.28 in contrast to ~ 0.33). The main distinguishing character to separate P. applanatum from P. pernai is the shape of the venter; while this is rounded in P. pernai, in P. applanatum it is slightly flattened and bordered by a narrowly rounded ventrolateral shoulder from the flanks.