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

Systematics Abbreviations to measurements in discoidal forms: H — total height; HI = height, measured just before widened peristome; HPW = height of penultimate whorl [measured at inner lip of (apparent) peristome]; D = maximum diameter of shell; W = width of peristome; AS = spiral angle; AU = umbilical angle; (linear measurements in mm, angles in °). Abbreviations to measurements in trochospiral forms — H total height; HL = height of last whorl; HP = height of peristome; D diameter of last whorl; W = width of peristome; AA = apical angle; AL = coiling angle of last whorl (if different from apical angle). Asterisks indicate reconstructed measurements taken on more (**) or less (*) damaged shell parts; (linear measurements in mm, angles in °). Abbreviations to measurements in cap shaped forms — H — total height; HA = height of the apex (if smaller than H); L = length of shell (anterior-posterior direction); LP — length of peristome; W = width of shell (perpendicular to length); (measurements in mm.). Class Gastropoda CUVLER, 1797 Subclass Archaeogastropoda THIELE, 1925 Order Euomphalina DE KÖNINCK, 1881 Superfamily Discohelicoiclca SCHRÖDER, 1995 Family Discohelicidac SCHRÖDER, 1995 Thoughts on the classification of Discohelix and morphologically related genera Recently many papers discussed Discohelix, its relatives, and the similarly shaped (more or less discoidal), but not closely allied genera and their classification on different suprageneric levels to accommodate them. In lack of sufficient data and owing to ambivalent evaluation of the known characters, the results seem to have still been far from the best solution. For long time Discohelix was placed into Euomphalidae, but MORRIS & CLEEVELY (1981) found that this superfamily contained genera of strongly different shell structures. They suggested a restricted interpretation for Euomphaloidea on an inferred shell structure of inner crossed-lamellar aragonite and an outer prismatic calcite layer. Traces of these shell layers were found in the shells of the Palaeozoic Amphiscapha (referring also YOCHELSON, WHITE & GORDON 1967) and Euomphalus. However, an unidentified Albian Discohelix species and some further Mesozoic genera from the previous Euomphaloidea were excluded on having nacreous inner shell layer. On these differences, they suggested a trochoidean systematic position to Discohelix and the other excluded genera. Unfortunately, these exclusions remained poorly documented; no identification of the studied Mesozoic species or publication of the actual shell structures supports these conclusions. Subsequently BANDEL (1988) and SCHRÖDER (1995) published similar results, based on a few studied specimens of two species with nacreous inner shell layer that they identified as Discohelix; the latter author erected Discohelicidae SCHRODER, 1995 to accommodate these forms. BANDEL's (1988) suggestion to exclude Discohelix DUNKER, 1847 from Euomphaloidea is derived from study of a Valanginian shell, in which he has found the inner shell layer nacreous. He identified the shell as Discohelix sp., however collabral riblets crossed the outer face between the outer (abaxial) angulations of the whorls, and this kind of riblets had been lacking from the character-set of Discohelix. The same type of riblets ornamented the Valanginian Discohelix bandeli SCHRÖDER, 1995. Fater KAIM (2004) identified both specimens as Adeuomphalus bandeli (SCHRÖDER, 1995) and this way he changed the family position of one of the conclusive species to Skeneidae (Trochoidea). SCHRODER (1995) also identified another species with nacreous inner shell layer as Discohelix sp. However, this is also a morphologically stranger species in Discohelix because it has a distinctly trochospiral earliest shell (of 0.64 mm diameter) with rather rapidly expanding whorls and an asymmetrical ornament comparing the spire and the umbilical sides. Though some authors (e.g. WENDT 1968) have extended the interpretation of Discohelix to involve also weakly trochospiral forms (~ Colpomphalus COSSMANN, 1916), SCHRODER'S species can not be regarded as member of this genus. Just the protoconch and the earliest teleoconch whorls of the Co/pompbalus-hke forms are planispiral and the trohospiral mode of coiling develops on subsequent whorls. The ornament of the spire and umbilical side should be (nearly) symmetrical, and the expansion rate of the whorls in true Discohelix (and Colpomphalus) is fairly smaller than that of the figured specimen. It means that no verifiable Discohelix species has yet been published with nacreous layer in its shell. In his survey, connected to the redescription of Discohelix calculiformis DINKER, 1847, GRÜNDEL (2005) also concluded that the nacreous shell layer has not yet been confirmed in Discohelix. In spite of this, he applied the family name "Discohelicidae" for a group of genera, and he evaluated the modified systematical arrangement of SCHRODER'S misidentified species ("Discohelix'' bandeli) by KAIM (2004) to Skeneidae as suggesting just a trochoidean relation of the Discohelicidae. But, does Discohelicidae exist after all? In reality, nacreous shell structure has not yet been confirmed not only in Discohelix but also in the group of morphologically closely related genera, which might be the further members of the possible family (sec them in: GRÜNDEL 2005). It means in fact that family Discohelicidae SCHRÖDER, 1995 of the original diagnosis is empty at present. The only specific character of Discohelicidae, the nacreous inner shell layer, should be identified first of all in