Loxoplocus ( Donaldiella ) karczewskii, Krawczyński, 2002

Krawczyński, Wojciech, 2002, Frasnian gastropod synecology and bio-events in the Dyminy reef complex of the Holy Cross Mountains, Poland, Acta Palaeontologica Polonica 47 (2), pp. 267-288 : 273-274

Loxoplocus ( Donaldiella) karczewskii sp. nov.

Fig. 6A–E .

Stegocoelia ( Hypergonia) sp.; Karczewski, 1980: 51, pl. 1: 5–6.

Holotype: GIUS 4−1293 /Pan−21 ( Fig. 6A ).

Type horizon and locality: Active quarry “Panek”, set B 3, the Detrital Beds; late Frasnian.

Derivation of the name: In memory of Dr. Leon Karczewski—investigator of fossil snails.

Material.—Fourteen spire fragments without a preserved aperture or older part of the shell ( GIUS 4−1285–1288/P13–16, 4−1292–1301/Pan−20–29).

Diagnosis.—High turriculate shell with rounded aperture; narrow distinctly prominent selenizone at the periphery of the whorl. Septation present in the older part of the spire. Loxoplocus ( Donaldiella) karczewskii sp. nov. differs from the type species L. ( Donaldiella) filosa ( Donald, 1902) by its more slender spire and more prominent selenizone. The Late Silurian L.( Donaldiella) morinensis Horný,1952 hasanoval aperture and a differing whorl profile.

Description.—Shell turriculate (about 10 cm in height), number of whorls unknown; shape of whorl distinctly angular; deep notch in center of outer lip, forming a narrow convex selenizone at the periphery of the whorl; growth lines prosoclinal above selenizone and opisthoclinal below it, base with orthoclinal growth lines; ornamentation consists of a strong spiral cord midway between the suture and periphery on the sutural ramp, anomphalous base with two spiral cords: the first one of which is just above suture and the weak second cord is situated between the periphery and lower suture; aperture rounded; protoconch unknown; septation common in the older part of the spire (see Fig. 15A ); pleural angle constant(about12°),variabilityofthetranslationindex( Hw / Ww) low ( Fig. 10 ).

Remarks.—The first specimens of this new species were described by Karczewski (1980) as Stegocoelia ( Hypergonia) sp. However, the narrow convex selenizone at the periphery proves assignment his specimens to family Lophospiridae . The genus Loxoplocus has been recognized from the Ordovician and Silurian as well as from the Early Devonian ( Horný 1952; Linsley 1968). The location of investigated specimens has allowed extension of the stratigraphic distribution of the genus Loxoplocus from the Ordovician to the late Frasnian.

Distribution.—Holy Cross Mountains: Panek, set B 3 (the Detrital Beds; late Frasnian).

Figures

Fig. 6. Loxoplocus (Donaldiella) karczewskii sp. nov. from late Frasnian Detrital Beds, Panek, set B3. A, B. Fragments of spire with well preserved ornamentation. C–E. Spires with visible septation and unpreserved ornamentation. A. Holotype, GIUS 4−1293/Pan−21. B. GIUS 4−1287/Pan−15. C. GIUS 4−1288/Pan−16. D. GIUS 4−1292/Pan−20. E. GIUS 4−1301/Pan−29. A–C, E. × 2. D. × 1.7.

Fig. 15. Late Frasnian limestones of the Detrital−Stromatoporoid Beds at Panek. A. Lagoonal wackestone with amphiporoids (a) and Loxoplocus (Donaldiella) karczewskii sp. nov. (L) with septation of spire, set B3, GIUS 4−1515/Pan−85. B. Reefal packstone−rudstone with the bivalve Megalodon sp. (M) and the gastropod Westerna subcostata (Schlotheim, 1820) comb. nov. (W), set B2. C. Oncoidal packstone with the thick−shell gastropod Westerna subcostata (Schlotheim, 1820) comb. nov., as oncoid nodule, and other unidentified gastropods (g), set B2, GIUS 4−1514/Pan−84. Scale bars 1 cm.

Fig. 10. Distribution of translation index (Hw/Ww) of Loxoplocus (Donaldiella) karczewskii sp. nov. from the late Frasnian of Panek (set B3).