Subgenus Pyrgopolon (Pyrgopolon) de Montfort, 1808
Description – Medium to large in size, the fixed tube portion fragile and rapidly increasing in diameter, commonly not preserved. The base usually shows well-developed cells, leaving a characteristic pattern on the surface of the substrate (see Pl. 5, fig. 1) after most of the tube has broken off. However, tubes without cells occur as well. There is no ‘Favosites structure‘ in contrast to P. (Septenaria). Perforate tabulae are present only in extant species, which were formerly referred to Sclerostyla, a synonym.
The free tube portion in fossil species either has seven longitudinal edges or keels, or lacks these; transverse wrinkles may occur. Recent species may show a different ornament. In fossil species, the middle layer of the tube wall in the posterior tube portion presumably was aragonitic and, thus, is usually dissolved, so that the cylinder layer can be moved freely inside the outer parable layer. The cylinder layer is thick walled at the posterior end and thin walled at the anterior.
The operculum is completely calcified, presumably aragonitic, and distinctly separated into a cucullus and a calcar. The cucullus is funnel-shaped, bearing radial striation; the calcar is slender, circular to triangular in cross section.
Pyrgopolon (Pyrgopolon) clava vittata (Regenhardt, 1961)next section
Pl. 5, figs. 3, 4.
Description – Small to medium sized, the smallest subspecies of the subgenus. The fixed tube portion is unknown, but should have been small. The free tube normally is curved like a horn, more rarely straight. The tube diameter rapidly increases up to 4.5 mm, but the diameter is reduced at the aperture. Seven longitudinal edges may be present only at the beginning of the free tube portion or lack completely. The transverse ornament may consist of wrinkled incremental striation and, sometimes, shallow swellings. The tube wall is thick near the aperture. The operculum is unknown.
Remarks – This subspecies never attains the size of the similar P. (P.) clava clava (Lamarck, 1818), which is known from the Mons Basin (southern Belgium), but is absent from the type Maastrichtian. A few finds of the fixed tube portion of an undescribed Pyrgopolon (Pyrgopolon) sp. indet. from the Vijlen Member (Pl. 5, figs. 1, 2) are much too large to be accommodated in P. (P.) clava vittata. Moreover, they have distinct transverse ornament. Presumably, these represent ancestors of P. (P.) regia regia (Regenhardt, 1961) (see below).
Distribution – Lower part of the Vijlen Member.
Pyrgopolon (Pyrgopolon) regia regia (Regenhardt, 1961)
Pl. 5, figs. 5-8.
Description – Medium sized. A fixed tube portion is present, but is rarely found. In the free tube portion seven strong longitudinal edges occur, which remain strong and distinct up to the aperture, in contrast to other species of P. (Pyrgopolon). The outer tube layer is massive or slightly porous, the tube wall being moderately thick. The operculum is unknown.
Distribution – Vijlen Member(?); Lixhe 1 to Gronsveld members. The total known range is early Maastrichtian(?); early late Maastrichtian.
Pyrgopolon (Pyrgopolon) mosae mosae de Montfort, 1808
Pl. 5, figs. 11-16.
Description – Medium sized to large. The fixed tube portion usually is cellular at the base, while the free portion is either straight or slightly curved; strongly curved tubes are rare, in contrast to P. (P.) clava. Most specimens lack any ornament. However, some may have a single longitudinal edge, or a furrow instead, or irregular furrows or edges, and show incremental lines or transverse wrinkles. The tube wall is thin. The cucullus of the operculum occasionally is strongly funnel-shaped, showing many non-denticulate ribs on the basal plate.
Distribution – Vijlen Member(?); Lanaye to Meerssen members; mass occurrences are known from the Nekum and basal Meerssen members. In the Kunrade limestone facies, however, P. (P.) m. ciplyana is the predominant subspecies. The total known range is late Campanian(?) (southern Sweden; in need of revision); early Maastrichtian(?); early late Maastrichtian to Danian (Geulhem Member). Probably missing from the Mons Basin
Pyrgopolon (Pyrgopolon) mosae ciplyana (de Ryckholt, 1852)
Pl. 5, figs. 9, 10.
Description – Medium sized to large. The fixed tube portion usually is cellular at the base, the free tube portion commonly being straight or slightly curved, rarely strongly curved. Seven strong keels are present in the posterior part of the free tube portion. Near the aperture, several transverse wrinkles or small ribs stand close to each other. The tube wall is thin. The cucullus of the operculum is low funnel-shaped, showing relatively few denticulate ribs on the basal plate.
Remarks – This subspecies has often been confused with P. (P.) m. mosae. Specimens named ‘Sclerostyla sp.’ by Jäger (1987, pl. 2, figs. 14-17 and, perhaps, fig. 13) belong to P. (P.) m. ciplyana. The operculum was named ‘Serpula instabilis’ by Wrigley (1952).
Distribution – Kunrade limestone facies at Kunrade and Benzenrade (equivalents of Lanaye to Emael members); these data were inadvertently omitted in Jäger (1998, p. 120). Moreover, this subspecies is known from the Meerssen Member of the main Maastricht ‘tuffaceous chalk facies’. The total known range is early Maastrichtian (obtusa Zone; Mons Basin) to Danian (Geulhem Member).