Cirsocerithium crassilabris ( von Koenen, 1885 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 82-83

Cirsocerithium crassilabris ( von Koenen, 1885)

Figs 23 P–S

1885 Scalaria crassilabris Koenen : 66, pl. 3, fig. 2.

1939 Eucycloscala ? crassilabris (v. Koenen)—Ravn: 58, pl. 2, fig. 1a–c.

1971 Scalina crassilabris (v. Koenen)—Rosenkrantz: 100.

Diagnosis. Protoconch with only three whorls, the last half whorl carrying spiral ribs. Teleoconch with around 12 transverse ribs on first whorl, increasing rapidly on later whorls. Aperture with very weakly developed siphonal canal.

Type material. The type material should include more than 30 specimens out of which one formed the basis of the drawings presented by von Koenen (1885: pl. 3: 2a–d) and got a museum number. This specimen, MGUH 865, is here selected as the lectotype. MGUH 865 is a nearly complete specimen only lacking the first whorl of the protoconch and the aperture ( Fig. 23R ).

Examined material. A single external and internal mould, MGUH 33131, from the Cerithium Limestone Member at Holtug, Stevns; a specimen ØSM.10042-61-a from the Korsnaeb Member at Korsnaeb, Stevns Klint; an informally catalogued mould SH.320 from the basal Cerithium Limestone at Højerup Church, Stevns Klint; the lectotype MGUH 865 from the Lellinge Greensand at Vestre Gasvaerk, and the complete specimen, MGUH 3751, figured by Ravn (1939: pl. 2: 1a–c) from the Lellinge Greensand at Sundkrogen, Copenhagen.

Type stratum and type locality. Black clay unit from the Lower Selandian Lellinge Greensand at Vestre Gasvaerk in Copenhagen .

Occurrence. Lower Danian Cerithium Limestone Member of the Rødvig Formation and up into the Lower Selandian Lellinge Greensand of eastern Denmark.

Description. Protoconch conical, consisting of three convex whorls, first 2 ½ whorls smooth with keel just above abapical suture. Last quarter whorl with three spiral ribs, one on the keel and two adapically of this. Transition to teleoconch fairly sharp. Teleoconch whorls convex, evenly rounded, weakly bicarinate with nearly continuous transition to base. Aperture subcircular with strong varix at outer lip and well developed callus and straight and sharp columellar fold partly hiding narrow umbilicus. No teeth or columellar folds present. Siphonal canal only weakly developed. Teleoconch sculpture initially consisting of three spiral ribs and approximately 12 coarse, slightly opisthocyrt transverse ribs, increasing in number to around 20 on fourth whorl and about 35 on fifth whorl. Sinus of transverse ribs located between two keels. Number of spiral ribs increasing gradually with ontogenetic growth. Low and coarse tubercles are formed at crossing points between transverse ribs and three to four primary spiral ribs, one or two of them located at adapical suture, while last two are found at keels. Base nearly smooth or covered by weak spiral ribs.

Measurements. Specimen MGUH 33131 from the Cerithium Limestone Member measures at least 9.7 mm in height and 5.0 mm in width, consisting of six teleoconch whorls.

Remarks. The early Danian specimen may differ from the type in having slightly less pronounced sculpture, by a higher number of transverse ribs on later whorls and in having a nearly smooth base. This kind of variation is however common in a normal population of living cerithiid gastropods ( Kase 1984) and the specimen is here regarded as conspecific with the Selandian Cirsocerithium crassilabris . C. crassilabris resembles somewhat the Early Cretaceous type species C. subspinosum Deshayes from France and the Mid Cretaceous C. collignoni Kiel, 2006 from Madagascar, but differs by the higher number of transverse ribs, by the weaker siphonal canal, by the lower number of protoconch whorls and by the absence of denticles in the aperture. The aperture and protoconch compares well with that of C. kulickii ( Schröder, 1995) from the Early Cretaceous of Poland (see Kaim 2004: fig. 25c), but the shell is easily distinguished by the protoconch only having three whorls, the last of which carries three and not two spiral ribs.

Figures

FIGURE 23. A. Arene jakobseni n. sp., Silicone cast of paratype MGUH 33120. Preserved width 8.9 mm. B–E. Ataphrus (Ataphrus) knoesensis n. sp. B–C. Silicone cast of holotype MGUH 33121. Width 4.0 mm. D. Silicone cast of paratype MGUH 33122. Width 4.2 mm. E. Silicone cast of paratype MGUH 33123. Width 3.9 mm. F–H. Cerithium sp. F. Silicone cast of MGUH 33124. Width 10.7 mm. G. Silicone cast of MGUH 33125. Width 9.9 mm. H. Silicone cast of MGUH 33126. Width 10.7 mm. I. Pseudovertagus? sp., Silicone cast of MGUH 33127. Width 1.6 mm. J–K. Striovertagus? sp., Silicone cast of MGUH 33128. Width 2.5 mm. L–O. Cerithidea? sp. L–M. Silicone cast of MGUH 33129. Cast height on figure L 7.4 mm. Cast width on figure M 3.3 mm. N–O. Silicone casts of MGUH 33130. Width 3.7 mm. P–S. Cirsocerithium crassilabris (von Koenen, 1885). P–Q. Silicone casts of MGUH 33131. Width 5.0 mm. R. Lectotype MGUH 865. Upper Palaeocene Lellinge Greensand, Denmark. Height 12.7 mm. Photograph by S. L. Jakobsen. S. Lateral view of MGUH 33132. Upper Palaeocene Lellinge Greensand, Denmark. Width 4.4 mm. T–U. Turritellid genus et sp. indet, Silicone cast of MGUH 33133. Width 1.0 mm. V–W. Turritella cf. plana Binkhorst, 1861. Silicone cast of MGUH 33134. Whorl width at least 17.2 mm. Height of last whorl 17.8 mm. X–Y. Mesalia danica n. sp. X. Silicone cast of holotype MGUH 33135. Width 2.2 mm. Y. Silicone cast of paratype protoconch MGUH 33136. Width 0.7 mm. Z. Mesalia sp., Silicone cast of MGUH 33137. Width 0.6 mm. AE. Tenagodus sp., Silicone cast of MGUH 33138. Width 4.3 mm.