Cranopsis cretacea, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 60-61

Cranopsis cretacea n. sp.

Figs 19 L–Q

2014 Fissurellinid gen. et sp. indet.; Hansen & Surlyk: 339, fig. 5: 18, tab. 3.

Diagnosis. Shell high with slightly anteriorly turned apex situated at highest point, one third from anterior margin. Trema long, reaching from just behind anterior margin, three quarters the distance to apex, bordered by strong and clearly convex flanks. Sculpture coarsely cancellate with 16 to 19 primary radial ribs.

Derivation of name. Refers to its Cretaceous age.

Type material. The holotype MGUH 33085 and paratype MGUH 33086 are preserved as internal and external moulds. The paratype is from Rødvig, Stevns Klint.

Additional material. The material consists of, in addition to the types, an internal mould in sample SR.986. A from the uppermost 15 centimetres of the Højerup Member at Rødvig, and an external and internal mould, ØSM.10042-257-a and b, housed at Østsjaellands Museum, also from the lithified top of the Højerup Member at Rødvig, Stevns Klint .

Type stratum and type locality. Lithified top of the upper Maastrichtian Højerup Member of the Tor Formation at Knøsen, Stevns Klint .

Occurrence. Upper 35 centimetres of the Maastrichtian Højerup Member at Rødvig and somewhere from the upper part of the Tor Formation, and here most likely the top of the Højerup Member at Knøsen, Stevns Klint.

Description. Shell high patelliform with bilateral symmetry. Protoconch turned slightly anterior, situated at top of shell approximately one third of shell length from anterior margin. Shell profile slightly concave anteriorly, becoming weakly convex behind apex. Flanks strong, weakly convex, nearly merging at anterior margin. Fissure long, narrow, pyriform, reaching from apex to slightly behind anterior margin with the widest part located half-way; interior side with well-developed, wide septum, reaching three quarters the distance from anterior margin to apex. Shell surface with sculpture of strong radial ribs cancellated by slightly weaker collabral ribs. The 16 to 19 primary radial ribs are intercalated by weaker secondary and tertiary ribs. External sculpture clearly seen on internal side.

Measurements. The largest specimen, holotype MGUH 33085, is 3.7 mm long, 3.0 mm wide and 2.5 mm high.

Remarks. Cranopsis cretacea n. sp. is somewhat variable with regard to its relative height, which may be distinctly less to slightly more than the width. The genus Cranopsis A. Adams is mostly represented by extant species, with a few fossil taxa known from Neogene deposits ( Wenz 1938; Knight et al. 1960). Cranopsis cretacea n. sp. thus becomes the by far oldest known representative from this genus.

Cranopsis cretacea n. sp. resembles species like the Northeast Pacific Cranopsis decorata Cowan & McLean, 1968 , but differs from any extant species by the combination of strongly developed concentric ribs and an anteriorly located apex, which is not recurved.

Figures

FIGURE 19. A–C. Acmaea selandica n. sp. A. Inner mould of holotype MGUH 33077. Length 5.9 mm. B. Paratype MGUH 33078. Length 2.6 mm. C. Internal mould of paratype MGUH 33079. Length 4.45 mm. D–E. Acmaea? sp. Wax cast of now lost specimen MGUH 33080. Length 19.7 mm. F–G. Cocculina? sp. Silicone cast of MGUH 33081. Exposed length 5.7 mm. H. Symmetrocapulus? sp., external mould MGUH 33082. Length 2.4 mm. I–K. Emarginula coralliora Lundgren, 1867. I–J. Silicone cast of MGUH 33083. Length 2.9 mm, height 1 mm. K. Inner mould of MGUH 33084. Length 7.8 mm. L–Q. Cranopsis cretacea n. sp. L–O. Silicone cast and inner mould of holotype MGUH 33085. Length 3.6 mm, width 2.6 mm. P–Q. Silicone cast and inner mould of paratype MGUH 33086. Length 2.1 mm. R–S. Palaeoloxotoma sp., Silicone cast of MGUH 33087. Length 17.2 mm.