Neobuchotrigonia gen. nov. y Buchotrigonia Dietrich (Bivalvia; Trigoniidae) en el Senoniano de Sudamerica

Abstract

RESUMEN. Se propone Neobuchotrigonia gen. nov., cuyas especies proceden de estratos del Senoniano de la costa pacifica sudamericana y se designa especie tipo a Buchotrigonia topocalmensis Perez y Reyes, del Campaniano superior de Chile. El nuevo taxon se caracteriza por tener concha grande a muy grande, gruesa, trapezoidal larga, area ancha, concava a moderadamente convexa, parcialmente ornamentada con costas transversas, en 'chevron' con las del flanco, carena marginal ausente, excepto en los primeros estadios de crecimiento, flanco compuesto por tres series de costas lisas o tuberculadas: excentricas, subverticales y concentricas; las dos ultimas, entrecruzadas en la zona posterior del flanco. Neobuchotrigonia gen. nov. se asigna a la subfamilia Buchotrigoniinae; habria derivado de Buchatrigonia a traves del aumento de tamano de la concha y disminucion de la superficie ocupada por las costas subverticales del flanco. Se consideran especies de Neobuchotrigonia gen. nov., ademas del tipo, a Trigonia hopkinsi Olsson, del Maastrichtiano de Peru y Neobuchotrigonia (?) jaillardisp. nov., del Santoniano (superior?)-Campaniano (inferior?) de Ecuador. Esta ultima especie posee valvas muy convexas, superficie areal plana, flancos con costas excentricas y subverticales tuberculadas, y concentricas predominantes, anchas y lisas. Se informa, tambien, acerca de la presencia de Buchotrigonia sp. en el Senoniano de Ecuador. ABSTRACT. Neobuchotrigonia gen. nov. and Buchotrigonia Dietrich (Bivalvia; Trigoniidae) from the Senonian of South America. The new trigoniid genus Neobuchotrigonia gen. nov. from the Senonian of South America, with the Chilean upper Campanian Buchotrigonia topocalmensis Perez y Reyes, as type species, is described in this paper. The new taxon is characterized by its shell large to very large in size, thick, elongate-trapeziform, wide area, concave to moderately convex, partly ornamented with transverse costae, which form 'chevron' with those of the flank, lacking a marginal carina except in early growth stages, flank with three series of costae, plain or tuberculate: eccentric, subvertical and concentric, the last two being intercrossed on the distal zone. Neobuchotrigonia gen. nov. is assigned to the subfamily Buchotrigoniinae, derived from Buchotrigonia through the increasing of shell size and decreasing of the surface occupied by subvertical costae of the flank. Besides the type species, Trigonia hopkinsi Olsson, from the Maastrichtian of Peru and Neobuchotrigonia (?) jaillardi sp. nov. from the (?Upper) Santonian-(?Lower) Campanian of Ecuador are considered as species of Neobuchotrigonia gen. nov. The last species has very convex valves, plain area, flank with eccentric and subvertical costae which are tuberculated and predominantly wide and plain concentric costae. Buchctrigonia sp. From the Senonian of Ecuador is also reported.