The studied strata represent lenticular bodies of green-gray calcareous marls full of ammonites and belemnites, occurring within a packet of Lower Oxfordian marls and marly limestones exposed in the quarry at Zalas, 25 km west of Krakow (Fig. 1). The strata rest on yellow to red marls of the Bukowskii Subzone of the Cordatum Zone and are overlain by grey spongy marls and marly limestones which are interpreted as transitional beds from the Lower Oxfordian (Cordatum Zone, Cordatum Subzone, elizabethae horizon) to Middle Oxfordian (Plicatilis Zone, Tenuicostatum Subzone, zalasiense horizon) 〚15〛, 〚18〛 and 〚19〛 (Fig. 2).

The ammonite assemblage from the Green Bed of Zalas represents lower part of the Cordatum Subzone. This dating is based on records of numerous cardioceratids, especially Cardioceras cordatum (Sowerby), C. asthonense Arkell, C. persecans (Buckman) 〚11〛 and 〚15〛 and some other characteristic species, as well as the stratigraphic position of this bed in the Lower Oxfordian section.

The green-grey marly beds, known as the Green Bed of Zalas, were subject of intense studies by Polish and French geologists since the beginning of the 1980s. A special attention should be paid to the role of French geologists in recognition of stratigraphic gaps at the boundary between the Lower and Middle Oxfordian in several sections in the Polish Jura Chain, including that from Zalas 〚10〛, and initiating a new phase in the studies of macrofossils of the Oxfordian in the Krakow region (southern Poland). Results of these studies were presented in a number of palaeontological and stratigraphic papers 〚1〛, 〚11〛, 〚14〛, 〚15〛, 〚16〛 and 〚20〛. The studies showed that sediments yielding the fossil assemblage from the Green Bed of Zalas were accumulated in a relatively short time interval, that is, during one biohorizon. Special attention should be paid to the results of synevolutionary analysis of ammonites of the families Aspidoceratidae, Cardioceratidae, Oppeliidae and Perisphinctidae, found in this bed. The analysis showed that morphological differentiation of representatives of some ammonite genera should not be interpreted as a result of condensation of the fauna, but rather as an intraspecific variability 〚11〛. Analysis of well-preserved representatives of the genera Mirosphinctes and Euaspidoceras, carried out by Bonnot et al. 〚1〛, showed that we might be dealing here with a dimorphic pair.

Attention should be also paid to traces of imprints of epifauna found on some moulds of ammonite body chambers. These imprints show continuation of growth of epifaunal organisms after the death of the ammonite 〚15〛 and 〚16〛. Taxonomical and taphonomical analyses of fossil assemblage of the Green Bed made it possible to evaluate shares of representatives of individual groups as well to define their preservation, the distribution and position of these fossil remains in sediment. Taphonomic analysis showed that any long-distant transport of these fossils might be excluded and that the individual ammonite assemblages appear fairly uniform which gives further support to the high rates of sedimentation of this layer 〚15〛.

In Europe, Lower Oxfordian ammonites, especially those of the Costicardia and Cordatum Subzones of the Cordatum Zone are still poorly known, because of widespread gaps and stratigraphic condensations in the studied sections. The studies carried out in the last two decades have shown that the section exposed in the Zalas quarry belongs to the most complete and, therefore, may be used as a reference section for further studies in Poland and other parts of Europe 〚19〛.

The studies gave a relatively rich collection of perisphinctids from the Green Bed at Zalas. The material gathered, dated well by the co-occurring cardioceratids and Taramelliceras and other ammonites, may greatly help in filling gaps in our knowledge of the evolution of this group. Intense palaeontological studies on these perisphinctids have been initiated in recent years and this article presents preliminary characteristics of the recorded assemblage and description of one new species. Detailed palaeontological descriptions of other taxa are being prepared.

See Fig. 4.

Holotype: Tables 1 (Zoological Museum of Jagiellonian University, No. 15883).

Type locality: Quarry at Zalas near Krakow.

Type lithologic horizon: Green Bed.

Age: Lower Oxfordian, Cordatum Zone, Cordatum Subzone.

Derivation of the name: to commemorate bicentenary of birth of Alcide d’Orbigny’and his contribution to the developments in stratigraphy of Phanerozoic rocks, especially the Jurassic.

Material: one complete fully grown specimen.

Diagnosis: complete macroconch with aperture preserved, 300 mm in diameter; body chamber occupying about 80% of the last whorl, high ovate in cross-section, with high vertical umbilical wall; ventral side poorly marked, smooth; body chamber ornamented with fairly uniform primary ribs, ridge-shaped and markedly bent forwards.

Description: mould preserved only from one side in marly limestone layer, displaying complete body chamber, the body chamber beginning at a diameter of 208 mm to end with peristome of diameter 300 mm; inner whorls ovate in cross-section, thicker than high, weakly overlapping one another, especially in the case of more external ones; umbilicus wide, with wall vertical and high at outer whorls, generally lower at inner whorls.

Inner whorls ornamented with regular well-developed rib, beginning on the umbilical margin, slightly prorsiradiate, bifurcating close to ventral margin. First order ribs with point of furcation situated low on the whorl side are occasionally found.

From the diameter of 130 mm onwards, ribs of the first order become thicker, better pronounced, and more distant from one another. They divide into secondaries close to the ventral margin. Ventral side of the penultimate whorl ornamented with secondary ribs similarly oriented but less well marked as primary ribs. Intercalaries are occasionally found.

The body chamber occupying three-quarters of the last whorl, weakly overlapping the penultimate one, with whorl section high ovate, higher than that of inner whorls. Ribs regular, strong, in the form of thick ridges, strongly bent forwards. Ventral side rounded, poorly marked, smooth. The last half of whorl ornamented with 18 thick, strongly prorsiradiate ribs.

Dm:– 300 mm, Wh: 70 mm, Wt: 46 (?) mm, Um: 185 mm. Ur/whorl: 175–47; 157– 50, 145–52.

Affinities: the above-described species resembles Perisphinctes (Arisphinctes) sp. A 〚M〛, recently described by Gygi 〚9 (p. 21, pl. 6, fig. 1, text-fig. 16, table 13)〛, differing from the latter in wider umbilicus and accordingly a more loose coiling of whorls. The species from Zalas also appears somewhat similar to P. (Arisphinctes) healeyi Neumann, differing in more strongly marked primary ribs, wider umbilicus and lower point of bifurcation of ribs.

It is still an open question whether or not the new species may be assigned to the subgenus Arisphinctes, in which Gygi 〚9〛 placed the possibly most closely related species Perisphinctes (Arisphinctes) sp. A 〚9〛 mentioned above. The record of representatives of this subgenus (similarly as those of the subgenus Dichotomosphinctes) may be treated as continuous from the Plicatilis Zone of the Middle Oxfordian, to become especially common in the Transversarium Zone 〚7〛 and 〚8〛.

Scarcity of material referable to that genus in strata of the Cordatum Zone may be due to failures in collecting of complete and fully grown large-size individuals due to the above mentioned gaps and condensations (G. Melendez, pers. comm.) or to a general trend in the reduction of size of ammonites, assumed by Brochwicz-Lewiński and Różak 〚5〛 at the turn of the Cordatum and Plicatilis Zones.