Metacerithium balticum ( Ravn, 1902 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 89-90

Metacerithium balticum ( Ravn, 1902)

Figs 24 H–K

1902 Cerithium balticum Forchhammer Ravn : 221–222, pl. I, figs 17–18.

1902 Cerithium Sartorii J. Müller ?—Ravn: 222, pl. I, fig. 19.

1923 Cerithium balticum Forchhammer—Jessen & Ødum : 44.

Diagnosis. Metacerithium with strongly transverse canal, broadly rounded periphery and base and three rows of relatively fine and sparsely distributed tubercles of semiequal strength.

Type stratum and type locality. Among the material used by Ravn (1902) for his description of this species only the two figured ( Ravn 1902: pl. I: 17–18) have been designated as types. They have the museum numbers MGUH 91 and MGUH 92, respectively. Both syntypes originate from the Cerithium Limestone Member at Stevns Klint. Ravn never selected a holotype for this species. Due to its better preserved spire and aperture specimen MGUH 91 is here selected as lectotype .

Material. MGUH 91 , MGUH 92 , MGUH 93 , MGUH 33144 , MGUH 33145 , ØSM.10042-40, ØSM.10042- 91-a, ØSM.10042-183-a–b and ØSM.10042-374-a. Another 133 specimens are catalogued by the unofficial sample numbers: SH.221, SH.228, SH.257 (2 specimens), SH.279, SH.281.A and C, SH.281.B–D, SH.281.C–D, SH.286, SH.288 (2 specimens), SH.289, SH.290, SH.294.A, SH.297.A, SH.297.A–B, SH.334.A, SH.342.A (3 specimens), SH.351.A, SH.352.A, SH.360, SH.372, SH.373.A–B, SH.380, SH.381.B–C, SH.385.B, SH.388, SH.390, SH.392, SH.394 (2 specimens), SH.396, SH.398, SH.399, SH.403.A–B, SH.407.A–B, SH.411 (2 specimens), SH.412, SH.413, SH.414.B, SH.415.A–B, SH.417, SH.418.A–B, SH.419.A–B, SH.419.B, SH.428, SH.436.A–B, SH.451 (4 specimens), SH.452 (2 specimens), SH.458.A, SH.460, SH.463, SH.470, SH.471, SH.473 (2 specimens), SH.483. C, SH.484.B, SH.517, SS.169, SR.143, SR.149, SR.152.A–B (2 specimens), SR.152.A, SR.210, SR.248, SR.271, SR,277.C, SR.286, SR.287, SR.288, SR.289, SR.295, SR.299 (2 specimens), SR.312, SR.315, SR.320, SR.358, SR.362, SR.373, SR.374 (2 specimens), SR.377, SR.387, SR.402, SR.406, SR.441, SR.446, SR.480, SR.501, SR.508, SR.510, SR.516, SR.527, SR.557.B, SR.562, SR.563, SR.566, SR.568, SR.581.A–B, SR.581.B, SR.583. A–B, SR.583.B, SR.610, SR.617.B, SR.623, SR.632, SR.638, SR.639 (2 specimens), SR.641, SR.642.A–B (2 specimens), SR.646, SR.656, SR.683, SR.684, SR.686, SR.698.A–B, SO.109, SO.186 (2 specimens), SO.187 and SO.188. A further 87 external and internal moulds from the Cerithium Limestone Member at Stevns Klint and four external moulds from Bundgaard near Rebild just south of the Limfjord, Jutland are found in the uncatalogued old collections at the Natural History Museum of Denmark .

Occurrence. Metacerithium balticum ranges from the lower part of the lower Danian Parvularugoglobigerina eugubina Partial Foraminiferal Range Zone (Pα) and up into the upper part of the Parasubbotina pseudobulloides Partial Foraminiferal Range Subzone (P1a) at Stevns Klint on Sealand and at least in some part of the informal ‘dead layer’ at Bundgaard, Dania and Vokslev quarries in the Limfjord area of northern Jutland. Stevns Klint: Rødvig (20–72 cm above the Cretaceous), Skeldervig, Harvig, Klintekongens Hule, Højerup (10–37 cm above the Cretaceous), North of Kirkevig, Kirkebraade, South of the Lighthouse, Barmhjertighedshuse Mandehoved, Holtug (44–64 cm above the Cretaceous) and North of Kulsti.

Description. Protoconch nearly 0.4 mm high and 0.4 mm wide, low conical with 2 ½ smooth and strongly convex whorls. Embryonic part moderately small. Transition to teleoconch marked by sinusigera riblet followed by strong transverse ribs and a slight median keel.

Teleoconch turriculate to slightly coeloconoid with up to at least 12 flattened whorls; initial whorls may appear convex due to transverse ribbing; whorls wide and low, the H/W ratio corresponding to between 0.35 and 0.40 on the later whorls. Suture deep and narrow. Last whorl featuring slight angle at transition to base; base flattened. Aperture rounded rectangular; columella slightly concave with no folds, terminated by nearly transverse canal directed parallel to lower margin of outer lip. Outer lip with three denticles somewhat removed from aperture, a weak one located on adapical part and two stronger ones situated on the flattened part close to the siphonal canal. A fourth strong denticle is located on the parietal lip closer to the aperture. Sculpture on first four to six whorls composed of 10 or more varix-like opisthocyrt ribs, which then begin to split up into two distinct spiral rows of tubercles, the abapical row located at periphery just above abapical suture, while adapical row runs approximately midway between the two sutures. The number of transverse ribs and tubercles increases slowly by about one per whorl. After the first four or five whorls a third adapical row of finer and slightly more densely spaced tubercles appears on a band or spiral rib at the adapical suture. The spiral rib increases in strength abapically, while the tubercle rows become less pronounced. Whorl surface covered by very fine spiral striae and forwardly concave growth lines with sinus between tubercle rows 2 and 3.

Measurements. Lectotype MGUH 91 is 11.4 mm wide and more than 25 mm high with 10 preserved teleoconch whorls, thereby representing one of the largest specimens known of this species.

Remarks. The name Cerithium balticum was used by Forchhammer (1861: p. 781) in his description of the Danian deposits of Denmark, but the name was first formalized forty years later when Ravn (1902) described the Danish gastropod fauna from Cretaceous and Danian deposits.

Figures

FIGURE 24. A. Tenagodus sp., Silicone cast of MGUH 33139. Tube diameter 5.6 mm. B–D. Campanile selandicum (Lundgren, 1867). B–C. Silicone cast of MGUH 33140. Width 11.4 mm. D. Silicone cast of MGUH 33141. Width 4.5 mm. E–F. Campanile sp. A. Silicone cast of MGUH 33142. Whorl height 2.1 mm. G. Campanile sp. B. Silicone cast of MGUH 33143. Height 4.2 mm. H–K. Metacerithium balticum (Ravn, 1902). H. Silicone cast of protoconch MGUH 33144. Width 0.45 mm. I. Silicone cast of MGUH 33145. Height 26.0 mm. J. Silicone cast of lectotype MGUH 91 figured by Ravn (1902, pl. I: 17). Width 11.7 mm. K. Silicone cast of MGUH 93, figured type for Cerithium sartorii Ravn, 1902. Height 7.1 mm. L. Dzikella? sp., Silicone cast of MGUH 33146. Width 6.0 mm. M–Q. Amaurellina ravni n. sp. M–N. Silicone cast of holotype MGUH 33147. Width 10.3 mm. O. The internal mould of paratype MGUH 33148. Width 13.2 mm. P. Paratype MGUH 33149, a mould with replaced shell. Height 12.8 mm. Q. Silicone cast of paratype MGUH 33150. Width of picture 3.0 mm. R. Trochocerithium sp., Silicone cast of MGUH 33151. Width 9.0 mm. S–W. Galericulus sp. S–T. Internal mould ØSM.10042-311. Length 5.8 mm. U. Internal mould MGUH 33152. Width 8.5 mm. V–W. Internal mould and external cast of MGUH 33153. Length 10.3 mm. Width of figure W 7.7 mm. X. Natica sp. A. Silicone cast of MGUH 33154. Width 7.9 mm.