Almadenorthis Reyes−Abril and Villas

Reyes-Abril, Jaime, Villas, Enrique & Gutiérrez-Marco, Juan Carlos, 2010, Orthid brachiopods from the Middle Ordovician of the Central Iberian Zone, Spain, Acta Palaeontologica Polonica 55 (2), pp. 285-308 : 288

Genus Almadenorthis Reyes−Abril and Villas nov.

Type species: Almadenorthis auriculata Reyes−Abril and Villas gen. et sp. nov.; lower Oretanian , Darriwilian, Middle Ordovician; central Spain .

Etymology: After the Almadén region, in central Spain, with important Palaeozoic fossiliferous localities where the first Spanish Ordovician orthids were discovered in the 19th Century.

Diagnosis.—Orthid with planoconvex, slightly sulcate to rectimarginate shell, with alate cardinal extremities, filate, capillate and coarsely ramicostellate ornament, short ventral interarea and divergent ventral vascula media.

Discussion.—These orthid shells do not fit within any of the defined genera in the family and merit formal taxonomic recognition. Within the family Orthidae , the most typical lateral profile is variably biconvex, planoconvex shells being only known in Orthis Dalman, 1828 . Nevertheless, the planoconvex Iberian shells can be clearly discriminated, in having a costellate ornament, which is usually costate in Orthis itself. The alate cardinal extremities of the new genus are unusual within the family, in which obtuse extremities are common, although it is a feature known also from Suriorthis Benedetto, 2003a and some species of Paralenorthis Havlíček and Branisa, 1980 or Sivorthis Jaanusson and Bassett, 1993 (see below). From Suriorthis and Paralenorthis , the new genus can be distinguished readily in having a planoconvex profile, while it is dorsibiconvex and ventribiconvex respectively in the other two genera. With Sivorthis the new genus has in common a costellate ornament plus an alate outline of some of its species, nevertheless its short interarea and divergent ventral vascula media are clearly different from the typically long interarea and parallel vascula media of Sivorthis .

Stratigraphic and geographic range.—The genus is known only from its type locality and type horizon.