Incanopsis fastigiata
Creators: name: DeVries, Thomas J.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Bivalvia
Arcoida
Incanopsis
Incanopsis fastigiata

description: Incanopsisfastigiata sp. nov.
(Figure 2 (a – c))
Diagnosis
Umbones one-quarter distance from anterior, posterior umbonal ridge very sharply angled. Cardinal area narrow.
Description
Shell length to about 20 mm, elongate, quadrate, inequivalve, posterior end truncate. Beaks located one-quarter shell length from anterior, strongly opithogyrate. Anterior sharply rounded; shell medially sulcate. Posterior umbonal ridge on left valve sharp and forming a 90° angle, passing at angle of 35° from dorsoventral axis towards posteroventral margin. Posterodorsal margin deeply depressed, flattened. Posterior umbonal ridge on right valve less angular, posterodorsal area less depressed. Radial sculpture of about 40 ribs anterior to posterior umbonal ridge, generally with every other radial rib inserted below umbonal area; about 20 radial ribs posterior to posterior umbonal ridge, generally equal in size. Radial ribs cancellate when crossing commarginal growth lines. Cardinal area narrow, smooth except ligamental area; full length not preserved. Ligamental area broadly triangular, includes entire cardinal area anterior to umbones; scored by at least 16 vertical ridges. Hinge plate not preserved. Ventral margin not preserved.
Remarks
Specimens of Incanopsisfastigiata sp. nov. differ from those of the late Campanian I. acariformis from the Tortuga Formation in the Sechura Basin of northern Peru (Olsson 1944) in the following characters: beaks of the new Caballas Formation species are situated closer to the anterior end of the shell; the posterior umbonal ridge is more sharply angled and the sharp angle extends for a greater distance ventrally; the number of radial ribs is double that of I. acariformis; the cardinal area is half the width of the cardinal area of I. acariformis; and the ligamental area is not set off from the cardinal area by deep grooves. The exterior form and sculpture of I. fastigiata resemble that of the northern Peruvian Arca (Barbatia) saladoensis Olsson, 1929; from the Chacra Formation, except that both umbonal ridges of the Caballas Formation species are more angular. Although the hinge and cardinal areas of specimens of the Chacra Formation species are not visible, the external characters indicate that Olsson ’ s (1929) arcoid species is a late early Eocene example of Incanopsis. The same may be true for a Barbatia sp. from lower lower Eocene beds of the Talara Basin (Woods 1922, 62, pl. 1, fig. 4).
Etymology
‘ Fastigiata ’, ‘ gabled roof ’, referencing the umbonal area of this species, which from a posterior perspective juts out in a gabled fashion from the steeply planar posterodorsal slopes of paired valves.
Material
UWBM 107752, holotype, left valve, B8772 (type locality), L (17.4), H 10.3, W (4.7); UWBM 107753, paratype, right valve, B8769, L (14.7), H (11.1); MUSM INV 234, paratype, right valve, B8769, L (12.8), H (9.8).
Occurrence
Lower Paleogene, Cuenca Member, Caballas Formation, East Pisco Basin, southern Peru.
description: Published as part of DeVries, Thomas J., 2019, Early Paleogene brackish-water molluscs from the Caballas Formation of the East Pisco Basin (Southern Peru), pp. 1533-1584 in Journal of Natural History 53 (25) on pages 1538-1540, DOI: 10.1080/00222933.2018.1524032, http://zenodo.org/record/3670229