Sassia faxense Ravn, 1933

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 103-104

Sassia faxense Ravn, 1933

Figs 26 Q–U

1902 Tritonium fenestratum n. sp. Ravn: 227–228, pl. II, figs 7–8.

1933 Tritonium (Sassia) faxense n. nom.—Ravn: 58–59, pl. V fig. 16a–b, pl. VI fig. 7a–b.

2014 Sassia faxense ( Ravn, 1933) —Lauridsen & Schnetler: 60, fig. 66A–D.

2014 Sassia sp.—Lauridsen & Schnetler: 60–61, fig. 67A–B.

Diagnosis. Shell relatively short, width typically around half the height. Protoconch small with 3 ½ to 3 ¾ whorls; last whorls covered by fine and closely spaced, prosocline collabral threads cancellated by a few, generally three, spiral threads. Teleoconch aperture taking up approximately half of shell height; columella only weakly concave. Teleoconch with strong reticulate pattern of sharp transverse and spiral ribs.

Material. In addition to the Faxe Quarry material stored at the Natural History Museum of Denmark, 70 moulds from the Cerithium Limestone , one from the basal Korsnaeb Member and 11 from the lithified top of the Højerup Member at Stevns Klint have been examined. These include specimens MGUH 33173, MGUH 33174, MGUH 33175, MGUH 33176, MGUH 33177, ØSM.10042-184-a–b, and the 26 informally catalogued specimens from samples SH.389, SR.568, SR.759.A–B, DN.22, SH.108, SH.185.A–B, SH.281.A and C, SH.284.A–B, SH.295. A–B, SH.302.A–B, SH.387, SH.447, SH.458.B, SH.516, SR.303.A–B, SR.393.A–B, SR.394, SR.482, SR.491, SR.529, SR.572.B, SR.613, SR.668.A–B, SR.911.A–B and SR.924.B. The rest are uncatalogued specimens deposited in the collections of the Natural History Museum of Denmark.

Type stratum and type locality. No holotype or lectotype was selected by Ravn (1902, 1933), but the type material was collected from the middle Danian Faxe Formation of Faxe Quarry.

Occurrence. Known from the lithified top of the Maastrichtian Højerup Member and the lowermost Danian Cerithium Limestone and Korsnaeb members at Stevns Klint, and from the middle Danian limestones of Faxe Quarry, Denmark. In Northern Jutland it has been found in the lower Danian ‘dead layer’ at Vokslev.

Description. Shell fusiform with tall, conical spire, shell width approximating half the height. Protoconch low conical, small, width typically around 1.3 to 1.7 mm, with 3 ½ to 3 ¾ convex whorls and low apex. Suture distinct. Last two whorls covered by fine and closely spaced, prosocline collabral threads (about 60 per whorl) cancellated by typically three narrow spiral cords. Transition to teleoconch abrupt, marked by coarsening of sculpture. Teleoconch somewhat variable regarding height and width, but with low to moderately convex and evenly rounded whorls. Suture adpressed. Varices broad and strongly raised, recurring approximately every 240˚ on teleooconch. Aperture, including siphonal canal, taking up between 45 and 53 % of shell height. Outer lip formed by strong varix with marked ridge running along inner side adapically, changing to outer margin abapically at transition to base of last whorl. Adapical transition to moderately wide callus smooth. Transition of outer lip to siphonal canal rather smooth with no sharp angle. Callus moderately thin, wide adapically, narrowing at transition to weakly concave columella, disappearing completely at short and left wards deflected deep siphonal canal. Number and strength of teeth on inner and outer lips quite variable. Inner lip typically carrying six teeth on columella and an additional six but weaker teeth on parietal lip. No folds. Outer lip carrying three teeth on abapical part and up to an additional three on adapical half.

Teleoconch sculpture of varying strength, strongly reticulate, consisting of sharp transverse and spiral ribs narrower than interspaces, and with tubercles at intersections. Each whorl carrying around 17 sharp transverse ribs, ribs slightly sigmoid with a prosocline, opisthocyrt adapical part. Primary spiral cords numbering 3–4 on spire whorls and about 10 on last whorl. Up to several fine spiral threads may be added between primary spirals on later whorls, most numereous on base.

Measurements. Specimens from the Cerithium Limestone Member may reach a height of at least 15.1 mm and a width of 10.7 mm, but most are less than 10 mm high.

Remarks. This species is somewhat variable with regard to protoconch size and the strength of the teleoconch sculpture, something which is seen for both the mid Danian and the latest Maastrichtian to earliest Danian material. The fine collabral threads on the protoconch are generally not preserved, but if present they number around 30 to 60 per whorl.

There is also some variation in the coarseness of the teleoconch sculpture and in the number of columellar and parietal teeth, where some specimens carry weak teeth on the transition between columella and the parietal region, while others are smooth in this area. This, though, is clearly intraspecific variation as a similar large intraspecific variation is found among recent species of Sassia.

Ravn (1902) originally named his new species Tritonium fenestratum , but later changed the name to Tritonium (Sassia) faxense Ravn, 1933 as Tritonium fenestratum Vincent, 1878 from the Eocene of Belgium had priority on the original name.

Figures

FIGURE 26. A–B. Alvania sp. A. Silicone cast of MGUH 33164. Width 1.5 mm. C. Alvania sp. B. Silicone cast of MGUH 33165. Width 0.8 mm. D. Zebina sp., Wax cast of MGUH 33166. Width 0.9 mm. E–H. Ceratia rodvigensis n. sp. E–F. Silicone cast of holotype MGUH 33167. Width 0.8 mm. G–H. Silicone cast of paratype MGUH 33168. Width 0.9 mm. I–J. Ceratia? sp. I. Mould of MGUH 33169. Width 0.9 mm. J. Silicone cast of MGUH 33170. Height 1.1 mm. K. Anchura sp., Silicone cast of MGUH 33171. Width 8.6 mm. L–M. Columbellaria tuberculosa (Binkhorst, 1861). Silicone cast of ØSM.10042-202-a–c. Width 5.2 mm, height 5.9 mm. N. Tylostoma? sp., inner mould MGUH 33172. Width 19.9 mm. O–P. Cassidae genus et sp. indet. Silicone cast and internal mould of ØSM.10042-315-a–b and c, respectively. Width 9.2 and 8.6 respectively. Q–U. Sassia faxense Ravn, 1933. Q. Detail of apex of MGUH 33173. Width of protoconch 1.4 mm. R. Silicone cast of MGUH 33174. Width 6.0 mm. S. Silicone cast of MGUH 33175. Width 6.5 mm. T. Silicone cast of MGUH 33176. Width 7.8 mm. U. Silicone cast of MGUH 33177. Width 5.2 mm. V–X. Hipponix sp. V–W. Internal mould MGUH 33178. Length 23.8 mm, width 19.5 mm. X. Inner mould MGUH 33179. Width 19.1 mm. Y–Z. Eulima? danica Ravn, 1933. Y. Silicone cast of MGUH 33180. Width 2.5 mm. Z. Silicone cast of MGUH 33181. Width 2.0 mm. AE. Eulima? sp., Mould MGUH 33182. Width 1.3 mm.