TAXONOMIC INTERPRETATION OF THE BUCHOTRIG ONIDS (BIVALVIA-TRIGONIOIDA) AND DESCRIPTION OF A NEW SPECIES OF SYROTRIGONIA FROM THE EARLY CRETACEOUS OF CHILE

The taxonomic relationships between buchotrigonids and other taxa of t he order Trigonioida are presented. It is proposed to classify Buchotr igoniinae at the level of family in the superfamily Myophorellacea, be cause of its wide area with transverse costae and marginal carina whic h may be partly or completely developed. The family Buchotrigoniidae i s divided into two subfamilies: Buchotrigoniinae (genera Buchotrigonia and Neobuchotrigonia) and Syrotrigoniinae nov. (genus Syrotrigonia). The Buchotrigoniinae is characterized by forms with tight excentric um bonal costae, flank-area ornamentation in 'chevron' with subconcentric and subvertical costae forming an L-shape on the anterior flank zone, or inter-crossed on the posterior zone of the flank. The Syrotrigonii nae is distinguished by its oblique umbonal costae, antecarinal depres sion and subconcentric and subvertical costae forming a V-shape or a m ore complex pattern. Syrotrigonia obesa sp. nov. is described from pos sible late Hauterivian-Aptian strata of Quebradas Las Breas and San An tonio, Coquimbo Region, Northern Chile. The new species is characteriz ed by its large, very convex and thick valves, and the presence on the lower middle of the flank of thick subconcentric costae of variable w idth.