Pleuriocardia (Incacardium) schneideri, 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 : 1550-1551

Pleuriocardia (Incacardium) schneideri sp. nov.

( Figure 3 (l – q))

Diagnosis

Shell ovate to elongate. Broad posterior sulcus extends from umbones to ventral margin. Ribs numerous with bulbous spines centred on ribs.

Description

Shell thin, to about 25 mm long, trapezoidal, H:L = 0.75. Subequilateral, umbones highly inflated; remainder of valves convex, excepting broad sulcus in front of weak posterior umbonal ridge and excepting irregular commarginal inflexions of curvature, especially ventrally. Beaks orthocline, orthogyrate on juveniles, overhanging hinge line; prosocline on adults. Posterior ligament narrow, less than half the length of posterodorsal margin. Dorsal margin sloping sharply anteriorly, less steeply posteriorly. Anterior broadly rounded; posterior with angled umbonal ridge. Anterodorsal and umbonal areas with 18 – 20 strong radial ribs, triangular in cross section, broader across middle of valve. U-shaped interspaces with weakly and irregularly raised commarginal growth lines. Posterodorsal flattened surface with 5 – 6 smaller triangular ribs, equal to each other in size. Circular or elongate bulbous spines or knobs rise from tops of radial ribs across middle three-fifths of valve; knobs more common at inflexions points, intersections with strong commarginal growth lines, and on specific radial ribs; other knobs randomly placed. Hinge plate and teeth not visible.

Remarks

Specimens of Pleuriocardia (Incacardium) schneideri sp. nov. differ from the Late Cretaceous type species, P. (Incacardium) mellisum Olsson, 1944 , in having fewer ribs in front of the posterior umbonal ridge (20 – 22, rather than 28) and interspaces that have a rounded profile, not triangular. The Caballas Formation species differs from the late Campanian to early Maastrichtian Pleuriocardia (Incacardium) trechmanni Schneider, 1999 , from Jamaica, in being longer than high, having fewer ribs anterior to the posterior umbonal ridge (20 – 22, rather than 25), and having nodes that are smaller, less bulbous, and more often aligned on the intersection of radial ribs with strong commarginal growth lines.

Etymology

Named in recognition of Jay A. Schneider, authority on the phylogeny of Incacardium and other cardiids.

Material

UWBM 107573 , holotype, left valve, B8772 (type locality), L (21.5), H 20.6, W (12.3) ; remainder are paratypes: UWBM 107574 , B8770, L 25.0, H 25.4, W 14.4 (pair) ; UWBM 107575 , B8769, L (13.7), H 11.8, W 11.5 (pair) ; UWBM 107576 , mould of left valve, B8769, L (25.5), H (19.4), W (4.9) ; MUSM INV 245 , B8772, L (19.1), H (19.1), W (9.2) (pair) ; MUSM INV 246 , mould of right valve, B8772, L (20.4), H (18.9), W (6.0) (pair) ; MUSM INV 247 , B8772, L (21.1), H (16.9), W (11.8) (pair).

Occurrence

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

Figures

Figure 3. Bivalves from the Caballas Formation. (a, b) Twig moulds on attachment scars of Ambigostrea sechura. (a) UWBM 107557, latex cast. (b) UWBM 107564, oyster length 11 mm. (c–e) Carolia (Parinomya) parinensis Olsson, 1928, on oyster attachment scars. (c) MUSM INV 243, latex cast of external mould on Ambigostrea sechura (MUSM INV 237), Carolia H 11.7 mm (top to bottom). (d) UWBM 107569, external mould on Ambigostrea sechura (UWBM 107559), Carolia H 22.9 mm (left to right). (e) UWBM 107570, external mould on Ambigostrea sechura (UWBM 107560), Carolia H 15.3 mm (left to right). (f–k) Incatina collinsae sp. nov., B8772. (f) UWBM 107637, holotype, L 13.7 mm. Right valve of pair, exterior. (g) UWBM 107637, left valve of pair, exterior. (h) UWBM 107637, paired valves, dorsal view. (i) UWBM 107638, paratype, L 10.0 mm. Right valve of pair. (j) UWBM 107639, paratype, L 16.4 mm. Right valve of pair. (k) UWBM 107638, left valve of pair. (l–q) Pleuriocardia (Incacardium) schneideri sp. nov. (l) UWBM 107575, paratype, B8769, L 13.7 mm. Paired valves, dorsal view, anterior to right. (m) UWBM 107574, paratype, B8770, L 25.0 mm. Right valve, exterior. (n) MUSM INV 247, paratype, B8772, L 21.1 mm. Right valve, exterior. (o) UWBM 107576, paratype, B8769, L 25.5 mm. External mould of left valve, oblique view. (p) MUSM INV 246, paratype, B8772, L 20.4 mm. External mould of right valve. (q) 107573, holotype, B8772, L 21.5 mm. Left valve, exterior. (r–t) Mulinoides plenicostatus sp. nov., UWBM 107571, holotype, B8769, L 28.1 mm. (r) Left valve, exterior. (s) Dorsal view, anterior on right. (t) Right valve, exterior.