Thyasira tessaria Olsson 1931: 53–54 Thyasira tessaria Conchocele Conchocele Thyasira Conchocele tessaria Conchocele species C. townsendi C. conradii C. tessaria ( Hryniewicz et al. 2017 ) C. taylori Hickman, 2015 C. tessaria Conchocele bathyaulax Hickman, 2015 C. tessaria C. kiritachiensis Hryniewicz, Amano, Jenkins, and Kiel, 2017 Conchocele tessaria Conchocele adoccasa ( Van Winkle, 1919 ) C. adoccasa C. tessaria C. taylori Conchocele tessaria ( Olsson, 1931 ) Mollusks and a crustacean from early Oligocene methane-seep deposits in the Talara Basin, northern Peru Kiel, Steffen Hybertsen, Frida Hyžný, Matúš Klompmaker, Adiël A. Acta Palaeontologica Polonica 2020 2019-12-06 65 1 109 138 7QS6S (Olsson, 1931) Olsson 1931 [808,1266,412,440] Bivalvia Thyasiridae Conchocele Animalia Lucinida 5 114 Mollusca species tessaria   Fig. 4.   1931  Thyasira tessaria sp. nov.;  Olsson 1931: 53–54, pl. 6: 10, 14.   Material.—  Six specimens( NRMMo187005–187010, Fig. 4) and several further unnumbered specimens (often fragmentary) from Cerro La Salinablocks 1, 4, 6–9, upper Oligocene, Talara Basin, Peru.  Description.—Small to medium-sized for the genus (L max. = 35 mm), inflation moderate (L/W ratio ca. 1.9), rounded-pentagonal in outline; beak prosogyrate, elevated and pointed, umbonal angle 90–100°; posterior fold deep but not sharp, increasingly curved in larger specimens, with resulting in shallow posterior sinus; a weak, secondary sulcus also present in some specimens; anterior margin narrow, demarcated by blunt ridge; lunule symmetrical and well-demarcated; escutcheon lanceolate; external surface sculptured by irregular, commarginal growth lines only. Hinge plate narrow, edentulous, ligament nymph broad and elongate; internal surface with fine radial striations developing tubercles near ventral margin.  Remarks.— Olsson (1931)described three thyasirid species from northern Peru:  T. peruvianaand  T. stauftifrom the Lomitos cherts, and  T. tessariafrom the Heath Formation at Pajarabobo, near Belén. Examination of Olsson’s (1931) typematerial at PRI showed that the specimens of all three species are more inflated than the material we collected; strongly so in the cases of  T. peruvianaand  T. staufti, and less so in the case of  T. tessaria. Based on the overall similarity of our specimens to  T. tessaria, especially their pentagonal outline, the broad posterodorsal area and the blunt posterior ridge, we considered the material reported here as belonging to  T. tessaria.  Thyasira peruvianadiffers from  T. tessariaby its much more prominent umbo, the much broader anterior margin, and the much smaller posterodorsal area.  Thyasira stauftidiffers from  T. tessariaby its deeper and sharper posterior sulcus, its narrower posterodorsal area, and its more oval outline.  Thyasira montanita( Olsson, 1931)from allegedly coeval strata in southern Ecuadorhas finer growth lines, a more rounded outline, a broader anterior margin, and a broader and shorter anterior adductor muscle scar (personal observations SK).    Thyasira tessariais here transferred to  Conchocelebased on its anteriorly situated beaks, the steeply sloping anterior margin, the weakly impressed lunule, and the broadly rounded posterior margin bearing a deep sulcus, characteristics of  Conchocelethat are not present in this combination in  Thyasira.  Conchocele tessariashows the following differences to other  Conchocelespecies:  C. townsendifrom Late Cretaceous strata on Seymour Island, Antarctica, has a similar pentagonal shape and narrow anterior margin, but has a deeper and sharper posterior fold ( Hryniewicz et al. 2017). The Paleocene  C. conradiifrom Svalbardis more inflated and has a longer anterior margin than  C. tessaria( Hryniewicz et al. 2017). Also  C. taylori Hickman, 2015, known from late Eocene to Oligocene strata of the North Pacific region, has a longer anterior margin, but its posterior fold is similar to that of  C. tessaria( Hickman 2015; Hryniewicz et al. 2017). Another late Eocene to Oligocene species is  Conchocele bathyaulax Hickman, 2015from Oregonand Washington state, USA; compared to  C. tessaria, it is much more inflated and has a more pointed, terminal umbo ( Hickman 2015; Hryniewicz et al. 2017). The late Eocene  C. kiritachiensis Hryniewicz, Amano, Jenkins, and Kiel, 2017, from a seep carbonate in Hokkaido, northern Japan, differs from  Conchocele tessariaby its rhomboidal shape, very broad anterior margin, and pointed, terminal umbo ( Hryniewicz et al. 2017). Finally,  Conchocele adoccasa( Van Winkle, 1919)from a Miocene seep deposit in Trinidadhas a broader anterior margin and a more distinct (sharper) posterior fold. This applies also to the specimens assigned to  C. adoccasafrom presumably Oligocene seep deposits of Colombia( Kiel and Hansen 2015). Overall, most similar to  C. tessariais the late Eocene to Oligocene  C. taylorithat is widespread along the North Pacific margin ( Hickman 2015; Hryniewicz et al. 2017).  Fig. 4. The thyasirid  Conchocele tessaria( Olsson, 1931)from early Oligocene seep deposits at Cerro La Salina (block 1, E; block 7, A–C; block 8, D), Talara Basin, northern Peru. A, B. Left valve of large specimen ( A, NRM Mo187005; B, NRM Mo187006). C. Medium-sized specimen (NRM Mo187007), right valve showing fine growth increments (C 1), dorsal view showing lunule (C 2), left valve showing dorsal sulcus (C 3). D. Small specimen (NRM Mo187008), left valve showing a healed shell injury (D 1), right valve showing dorsal sulcus (D 2) and dorsal view showing lunule posterior area (D 3). E. Small specimen (NRM Mo187010) showing hinge of right valve.  One specimen(NRM Mo187008) shows two indentations on LV, which might represent a failed attack by a predator such as a durophagous crustacean. Damage to fossil seep mollusks attributed crustaceans has been noted previously (e.g., Kiel et al. 2016, and references therein, Klompmaker et al. 2018).   Stratigraphic and geographic range.—Early Oligocene of the Talara Basin, northern Peru. NRM Peru Talara Basin Cerro La Salina upper Oligocene 5 114 6