Rhombopsis Gardner, 1916

DeVries, Thomas J., 2019, Early Paleogene brackish-water molluscs from the Caballas Formation of the East Pisco Basin (Southern Peru), Journal of Natural History 53 (25), pp. 1533-1584 : 1571

Genus Rhombopsis Gardner, 1916

Type species: Fusus newberryi Meek and Hayden, 1857 , by original designation. Cretaceous, Nebraska, USA.

Remarks

Rhombopsis was proposed by Gardner (1916, 456) in mid-paragraph, stating a belief that (1) Maryland ‘ fulguroids ’ could not be placed in Pyrifusus Conrad, 1858 (s.s.); (2) that the Maryland taxa could be grouped with a subset of Pyrifusus species exhibiting sinuous outer lips and flattened columellas, as defined by Meek (1876); (3) the subset deserved more than the subgeneric rank created by Meek (1876); and (4) Meek ’ s (1876) name for the species subset, Neptunella subgen. nov., was preoccupied by Neptunella Gray, 1854 , a ranellid gastropod, and so needed to be replaced – by Rhombopsis . The reader might infer that subsequently described fulguroid Maryland species ( Gardner 1916, 457 – 463) were considered examples of the newly elevated and renamed Neptunella , i.e. Rhombopsis , although Gardner (1916) still used Pyrifusus in her description of the Maryland species: P. marylandicus sp. nov., P. vittatus sp. nov., P. monmouthensis sp. nov., P. cuneus Whitfield, 1892, P. whitfieldi sp. nov., and P. elevata Whitfield, 1892 .

Sohl (1964) addressed the scope of the genus Rhombopsis in his monograph on Late Cretaceous molluscs from Tennessee and Mississippi. From a number of Maryland species, Sohl (1964, 196) accepted only Pyrifusus marylandicus Gardner, 1916 as an example of Rhombopsis . Later on, Sohl (1964, 199) distinguished between Rhombopsis and the closely related Deussenia Stephenson, 1941 , on the basis of the presence of a strongly developed subsutural collar (weak or absent on the former genus, strong on the latter genus). Nevertheless, Sohl (1964) proceeded to describe a new species, R. molinoensis , with a broad subsutural collar. The figures of R. molinoensis ( Sohl 1964, pl. 24, figs. 14, 15) are biconic, rather than fusiform, and have a uniformity of spiral sculpture (narrow primary spiral cords from the base of the subsutural collar to the tip of the siphonal canal, all crossing the axial ribs) also seen in the type species of Rhombopsis , R. newberryi (see Stanton 1920, pl. 7, fig. 8a, 8b). These characters are not seen in a figure of the Late Cretaceous species from Tennessee, Rhombopsis ? [sic] orientalis Wade, 1926 ( Sohl 1964, pl. 24, fig. 5), nor in figure of the Late Cretaceous R. gracilis (Stanton, 1920) from North Dakota.

Sohl (1964, 199) questioned Olsson ’ s (1944) assignment to Rhombopsis of the Late Cretaceous species, R. meridionalis Olsson, 1944 , from the Tortuga Formation of northern Peru, based on a siphonal canal curved to a greater extent than seen in North American Cretaceous species.

The proper separation of these small Late Cretaceous fasciolariids (or melongenids) is beyond the scope of this study. It can be noted that among the taxa falling within the scope of discussion addressing Rhombopsis , there is a subset of species with fusiform profiles, a weak or absent subsutural collar, and primary and secondary spiral cords: R. gracilis , R. orientalis (Tennessee) , R. marylandicus (Maryland) , and R. meridionalis (northern Peru). Late Cretaceous specimens from the central Peruvian Andes tentatively assigned to Rhombopsis by Berry and Singwald (1922) do not resemble any taxa of Rhombopsis , whether the genus is defined broadly or narrowly.