Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 26. 2008. (Budapest, 2008)

Shape — Dextral, depressed, discoidal form with concave spire. On spiral side of almost bilaterally symmetrical shell, protoconch ("apex") slightly raises. Axial whorl section rounded in protoconch, but nearly trapezoidal with feebly convex sides on subsequent whorls. Spiral angulations, delimiting outer face, sharp and carinate throughout whole teleoconch. Peristome usually damaged. Single, probably mature, Bakony Mts fragment of 42—44 mm reconstructed diameter shows quadrangular peristome, slightly broadened in every direction, except adaxially. Sculpture — Approximately half whorl after nucleus, spiral lines appear on protoconch and persist along about two whorls then fade away as observed in relatively well-preserved Bakony Mts specimen. No sharp boundary found between protoconch and teleoconch. From third whorl, carina visible both on spire and umbilical sides on all whorls along abaxial sutures. About two whorls after end of early lineation, spiral ornament reappears. It consists of fine, regularly spaced threads occurring on whole whorl surface. Growthlines visible slightly earlier than reappeared spiral ones of teleoconch. On post-juvenile whorls, irregularly spaced and strengthened, but rather dense, low, collabral ridges appear on spiral and umbilical sides. With onset of visible growth-lines, carinae of outer angulations become (usually irregularly) corrugated; corrugation endures up to peristome and its strength increasing like that of collabral ridges; corrugation may become obscure on latest whorls. Remarks — Discohelix orbis is interpreted here by the specimens found in STOLICZKA (1861) "originals collection". The selected neotype represents the typical shell of the species. Its shape, measurements and ornament well correspond to REUSS (1852) description and figuration, excepting that REUSS's drawings show much sparser and stronger nodulae on the carinae of the outer angulations. In the studied abundant material, only two comparable specimens occurred with sparser and stronger nodosity but they also differ in the shape and the measurements. These characters distinguish them on species level (see Discohelix pseudomelia n. sp. below). (REUSS's description and DUNKER's notice about the strong similarity to D. calculiformis, discussed in the next paragraph, suggest that the original drawings are probably not realistic.) Table 1 — A comparison of Discohelix calculiformis DUNKER, 1847 and Discohelix orbis (REUSS, 1852). — The compared characters are observed on specimens of about 30 mm diameter. character compared Discohelix calculiformis Discohelix orbis spiral ornament on protoconch absent (WENDT 1968); not visible owing to poor preservation (GRÜNDEL 2005) found on Bakony Mts specimens (SZABÓ 1979) number of whorls (at same diameter) ~7 (GRENDEL 2005) 9-10 m STOLICZKA (1861) originals number of corrugations on carinae of outer angulations 80 (penultimate whorl of lectotype) (GRÜNDEL 2005) 180-200, when distinguishable on penultimate whorls of STOLICZKA (1861) originals fine spiral threads on teleoconch only at carinae of outer angulations (GRÜNDEL 2005) dense on whole surface of whorls in STOLICZKA (1861) originals growth lines hardly visible (GRÜNDEL 2005) marked in STOLICZKA (1861) originals subregularly repeating collabral ridges absent (GRÜNDEL 2005) present on spire and umbilical sides in STOLICZKA (1861) originals As editor of the Palaeontographica, DUNKER attached notices to REUSS's (1852) paper to express his opinion that D. orbis is probably identical with D. calculifom/is DUNKER, 1847, the type species of the genus. Subsequently, in spite of the similarity and a rather large number of publications, dealing with these species, the distinction of D. orbis from D. calculiformis remained uncertain. First WENDT (1968) suggested some characters for this purpose (see Table 1) and further differences can be found in GRÜNDEL (2005) paper that provided a new description to D. calculiformis on the basis of the syntypes and QUENSTEDT's (1881-1884) finds. GRÜNDEL (2005) did not compare the two species, but accepted D. orbis by listing it with the existing further species of the genus. A comparison of the two species is necessary

7 not only owing to the morphological similarity, but also the similar stratigraphical distribution. Both species are known from Pliensbachian strata (D. orbis also from Upper Sinemurian); however, their palaeobigeographical distribution seems different. D. orbis is an "index" species for the Pliensbachian Mediterranean Province while D. calculiformis has been found in "stable European" strata of a restricted area in Germany. GRÜNDEL'S (2005) re-description and photos provided much more morphological details to a comparison than all former publications. The two species are really similar to each-other but some differences support their distinction (see Table 1). Further distinction problems to discuss arise from STOLICZKA (1861) decision about unification of Discohelix ornata (HÖRNES, 1853) with Discohelix orbis (REUSS, 1852). Because STOLICZKA's (1861) figures about Discohelix ornata (Tafel III. Fig. 8, Fig 9) are composed of specimens of two species, it means two necessary

7 comparisons. Obviously, a part of the specimens must bear the original name but the