Chilodonta rudis ( Binkhorst, 1861 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 70-71

Chilodonta rudis ( Binkhorst, 1861)

Figs 21 L–Q

1861 Turbo rudis Binkhorst : 49, pl. III, fig. 8a–b.

1861 Turbo detritus —Binkhorst : 45–46, pl. III, fig. 10a–b.

1861 Turbo bidentatus —Binkhorst : 46, pl. III, fig. 9.

1898 Trochus (Craspedotus) rudis Binkhorst—Kaunhowen : 38–39, pl. II, figs 1–3.

1986 Chilodonta (Chilodonta) rudis ( Binkhorst, 1861) —Abdel-Gawad: 89, pl. 2, figs 7–8.

2014 Chilodonta rudis (Binkhorst van den Binkhorst, 1861) —Hansen & Surlyk: 339, fig. 6: 5, tab. 3.

Diagnosis. Low conical; whorls weakly convex, keeled; aperture with three strong denticles on outer lip, a parietal denticle and strong columellar fold; whorl sculpture relatively fine, adapically consisting of well developed, sharp transverse ribs cancellated by weaker spiral ribs and abapically with transverse ribs or just fine and densely spaced collabral threads cancellated by coarser spiral ribs.

Material. The Danish material consists of MGUH 33103 to MGUH 33106, the informally numbered SR.728, SR.756, SR.924.A, SR.954, SR.1069.A and SR.1071.A–B, together with five internal and external moulds lacking numbers in the old collections of the Natural History Museum of Denmark.

Type stratum and type locality. The holotype figured by Binkhorst (1861) on plate III: 8a–b was collected from the upper Maastrichtian stratotype at Limburg, the Netherlands.

Occurrence. Lithified top of the Højerup Member of the Maastrichtian Tor Formation at Stevns Klint (Rødvig, Skeldervig, Mandehoved, Holtug Quarry and Kulsti Rende). A single specimen coming from the lower Danian Cerithium Limestone Member at Stevns Klint has been examined in the collections of C. Heinberg, Denmark ( Fig. 21Q ), but it may be reworked from the Maastrichtian deposits. Outside of Denmark it is known from the Maastrichtian of Poland and the Netherlands ( Abdel-Gawad 1986).

Description. Shell small, low conical with a spire angle of between 65˚ and 75˚ and up to around five whorls. Protoconch nearly planispiral, consisting of approximately one smooth whorl with a small initial whorl. Protoconch width around 0.25 mm.

Teleoconch sharply rounded at midwhorl, keel separating weakly convex adapical and abapical side; suture distinct, located just below keel of preceding whorl with the two whorls meeting at an angle of approximately 90˚. Shell narrowly umbilicate in smaller specimens, becoming covered by parietal callus in larger shells. Aperture with a fairly strong columellar fold or elongated denticle on lower columella, a strong parietal ridge or denticle and three strong denticles on the outer lip distributed with one above keel and two below. Teleoconch sculpture adapical to keel consisting of strong, sharp, densely spaced transverse ribs with 5 to 8 weaker spiral ribs (increases with size), sometimes intercalated with secondary ribs. Abapical side with spiral ribs cancellated by fine, densely spaced collabral threads.

Measurements. The most complete Danish specimen MGUH 33103 is 6.0 mm wide and 5.8 mm high with about 5 1/3 teleoconch whorls in addition to one protoconch whorl.

Remarks. The type material of Chilodonta rudis ( Binkhorst, 1861) from the Netherlands appears in general to be characterized by coarser transverse sculpture on the base of the last whorl than is typical for the Danish material, but otherwise they seem identical.

Figures

FIGURE 21. A–B. Leptomaria meyeri Pacaud, 2004. Silicone cast and inner mould of MGUH 33097. Width of cast 14.5. Width of inner mould 11.4 mm. C–H. Bathrotomaria jakobseni n. sp. C–F. Silicone cast and inner mould of holotype MGUH 33098. Width of exposed shell 21.3, 21.3, 15.6, 17.3 mm respectively. G. Outer mould of paratype MGUH 33099. Preserved radius 4.4 mm. H. Silicone cast of last whorl of paratype MGUH 33100. Width 16.2 mm. I. Bathybembix? sp., Silicone cast of MGUH 33101. Width 3.65 mm. J–K. Danilia sp., Silicone cast of MGUH 33102. Width 1.25 mm. L–Q. Chilodonta rudis (Binkhorst, 1861). L–M. Silicone cast of MGUH 33103. Width 6.0 mm for complete specimen, 0.25 mm for protoconch. N–O. Silicone cast of MGUH 33104. Width 7.35 mm. P. Silicone cast of aperture MGUH 33105. Height 4.8 mm. Q. Silicone cast of MGUH 33106. Width 4.65 mm. R–T. Eucycloscala gracilicostatus n. sp. R. Silicone cast of paratype MGUH 33107. Width of fragment 1.3 mm. S–T. Silicone cast of holotype MGUH 33108. Width 2.3 mm. U. Phorcus sp., Silicone cast of MGUH 33109. Height 3.2 mm, exposed width 2.2 mm.