Rhombopsis longinquus, DeVries, 2019

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 : 1572

Rhombopsis longinquus sp. nov.

( Figure 5 (j), 5(k), 5(m), 5(n))

Diagnosis

Fusiform, with well-defined sutural ramp and subsutural collar weak or absent. Axial ribs and growth lines sinuate. Spiral cords numerous, vary in strength across mid-section of last whorl.

Description

Shell length to about 25 mm, fusiform with and moderately high spire and long anterior canal. Protoconch unknown. Teleoconch with four or five convex whorls with sutural ramp, and sharply rounded shoulder. Subsutural collar weak or non-existent; periphery at or just below shoulder angle. Sutures appressed. Axial sculpture of about 11 ribs extending length of spire whorls but fading on sutural ramp and below periphery on last whorl. Ribs and growth lines sinuate with broad sulcus centred on periphery. Spiral sculpture of weakly scabrous spiral cords and threads: about seven strong threads on ramp; spire whorls and peripheral area of last whorl with weak primary spiral cords and intervening threads, numbering one to three; remaining anterior of body whorl with about 15 weak primary spiral cords. Spiral cords and some threads cross axial ribs. Anterior canal poorly preserved. Siphonal fasciole present, poorly preserved. Parietal wall without callus; columella straight, slightly excavated. Posterior canal absent. Outer lip and growth lines sinuate.

Remarks

When compared with Olsson ’ s (1944) figured specimen of Rhombopsis meridionalis , specimens of R. longinquus sp. nov. are more sharply shouldered and the axial ribs are more pronounced at the periphery and shoulder. Details of the spiral sculpture are identical.

Etymology

‘ Longinquus ’, Latin adjective for ‘ remote ’, referencing the fact that nearly all other species of Rhombopsis occur in Cretaceous strata of North America ( Sohl 1964).

Material

UWBM 107630 , holotype, B8772 (type locality), L (18.3), W (11.6) ; remainder are paratypes: UWBM 107631 , B8772, L (22.5), W (14.9) ; UWBM 107632 , B8769, L (16.4), W (10.8) ; MUSM INV 269 , B8769, L (19.9), W 12.6 ; MUSM INV 270 , B8769, L (20.3), W 11.9.

Occurrence

Lower Paleogene, Cuenca Member, Caballas Formation, East Pisco Basin, southern Peru.

Figures

Figure 5. Gastropods from the Caballas Formation. (a–e) Caballasea segmentata gen. nov., sp. nov. B8769. (a) UWBM 107607, paratype, L 12.4 mm, apertural view. (b) UWBM 107607, abapertural view. (c) UWBM 107606, holotype, L 12.6 mm, abapertural view. (d) MUSM INV 262, paratype, L 8.3 mm, oblique view of parietal callus and columella. (e) UWBM 107608, paratype, L 15.3 mm, abapertural view. (f, g) Turritella capistrata sp. nov. (f) MUSM INV 259, paratype, B8772, L 16.3 mm, lateral view. (g) UWBM 107601, holotype, B8770, L 14.4 mm, apertural view. (h) Turritella saposa Olsson, 1944, UWBM 107602, B8770, L 15.5 mm. (i) Cristispira caballasensis sp. nov., UWBM 107605, holotype, B8769, L 5.1 mm, fragment. (j, k, m, n) Rhombopsis longinquus sp. nov. (j) UWBM 107630, holotype, B8772, L 18.3 mm, apertural view, outer lip missing. (k) MUSM INV 269, paratype, B8769, L 19.9 mm, abapertural view. (m) UWBM 107631, paratype, B8772, L 22.5 mm, abapertural view. (n) UWBM 107632, paratype, B8769, L 16.4 mm, lateral view of spire and columella. (l, o–q) Tristeirostoma saxaquadrata sp. nov. B8771. (l) UWBM 107636, paratype, L 10.0 mm, spire. (o) UWBM 107,635, holotype, L 7.6 mm, abapertural view. (p) UWBM 107635, lateral view of columella. (q) UWBM 107635, apertural/lateral view.