Hokkaidoconcha, Kaim, Jenkins & Waren, 2008

Nakrem, Hans Arne, 2017, Gastropods from the Late Jurassic - Early Cretaceous seep deposits in Spitsbergen, Svalbard, Zootaxa 4329 (4), pp. 351-374 : 358-359

? Hokkaidoconcha sp.

( Fig. 6E–I )

Description. Abyssochrysoid shells ornamented with strong orthocline axial ribs which do not reach the suture adapically and with numerous spiral riblets which cross over the axial ribs. Growth lines prosocline. Whorl flanks are weakly inflated and the suture moderately incised. Protoconch and aperture not preserved.

Material and occurrence: Three specimens preserved as external moulds from seep #3 (all illustrated: PMO 224.759–761); Sassenfjorden, Svalbard; late Tithonian, Late Jurassic.

Remarks.? Hokkaidoconcha sp. is represented only by shell fragments and several features (e.g. protoconch, aperture) could not be observed in the available specimens. This is why we decided to leave this species in open nomenclature. Similar shells have been described by Sohl (1960) from the Late Cretaceous of the USA as species of Melanatria : Melanatria ? cretacea Wade, 1926 and Melanatria ? sp. The genus Melanatria Bowdich, 1822 is considered to be an objective synonym of Pirena Lamarck, 1822, which in turn is a synonym of Faunus Montfort, 1810 (for details see Köhler & Glaubrecht 2010). In the past, the type species of Melanatria was repeatedly wrongly cited as Buccinum flumineum Gmelin, 1791 (e.g. Sohl 1960), which is now interpreted as nomen dubium ( Köhler & Glaubrecht 2010) but previously synonymized with the modern freshwater pachychilid cerithioidean Madagasikara spinosa ( Lamarck, 1822). The latter species (and the entire genus Madagasikara) is endemic to Madagascar ( Köhler & Glaubrecht 2010). It is therefore rather unlikely that this genus is present in the marine deposits either in the Late Jurassic of Spitsbergen or Late Cretaceous of the USA. Instead, we think that all these shells may represent an as yet undescribed genus of abyssochrysoids similar to Hokkaidoconcha . We do not attempt to describe a new genus here because of the poor preservation of the available material and we temporarily place it in Hokkaidoconcha , pending better material becoming available.

Figures

FIGURE 6. A – D. Abyssomelania sp. (PMO 224.758), Seep deposit # 3, Sassenfjorden, Svalbard; late Tithonian (Late Jurassic). E – I.? Hokkaidoconcha sp., Seep deposit # 3; late Tithonian (Late Jurassic). E. PMO 224.759. F, G. PMO 224.760. H, I. PMO 224.761.