Cristispira caballasensis sp. nov. (Figure 5 (i)) Diagnosis Hypercampanulate; three strong keeled spiral cords on anterior two-thirds of spire whorls; finely spirally threaded interspaces. Description Shell small; pleural angle about 12°. Whorls hypercampanulate, sutural area deeply concave. Protoconch unknown, number of whorls in spire cannot be estimated. Spiral cords keeled; spiral formula dCBAr; primary cords about equally strong. Spacing formula C14B45A67; n = 1). Interspaces with microscopic spiral threads. Lateral growth line orthocline; posterior inflexion absent, anterior inflexion barely discernible. Lateral sinus moderately deep, apex close to spiral cord B. Base and aperture not preserved. Allmon formula?-1-M-B-OR. Remarks The elements of the spiral sculpture of Cristispira caballasensis sp. nov., evident even from the partial single specimen available, are nearly identical with those of two Peruvian species, the Late Cretaceous C. prechira (Olsson, 1944) and the middle Eocene C. paracasensis (Rivera, 1957): three keeled primary spiral cords, a deeply con- cave sutural area, wide concave interspaces with microscopic spiral threads, and in some specimens a secondary spiral cord or thread near the posterior suture. The spacing formula for C. caballasensis (C14B45A67; n = 1) does differ from that of the younger C. paracasensis (C35B58A72; n = 8; DeVries 2007) but is the same as that for the older C. prechira (C14B40A69; n = 1). The strength of the anteriormost primary spiral cord of C. caballasensis, however, is like that of C. paracasensis, i.e. much stronger than the anteriormost primary spiral cord of C. prechira. Material UWBM 107605, holotype, B8769 (type locality), L (5.1), W (4.4). Occurrence Lower Paleogene, Cuenca Member, Caballas Formation, East Pisco Basin, southern Peru.

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 page 1570, DOI: 10.1080/00222933.2018.1524032, http://zenodo.org/record/3670229