Early Paleogene brackish-water molluscs from the Caballas Formation of the East Pisco Basin (Southern Peru) Author DeVries, Thomas J. text Journal of Natural History 2019 2018-12-17 53 25 1533 1584 journal article 24019 10.1080/00222933.2018.1524032 034ebcd9-efa7-416a-822c-b6aee0e57a1c 1464-5262 3670229 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 .