Gutiorthis 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 : 290

Genus Gutiorthis Reyes−Abril and Villas nov.

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

Etymology: Named after our co−author Juan Carlos Gutiérrez−Marco, who made a great part of the brachiopod collection, and for his stratigraphical and palaeontological studies on the Spanish Ordovician.

Diagnosis.—Orthids with ventribiconvex shell of suboval outline and obtuse cardinal angles in adults; ornamentation costate, capillate and filate. Ventral valve with subtriangular muscle field and saccate mantle canal system; vascula media parallel and adjacent to anterior third of valve. Dorsal valve with high and strong notothyrial platform, thin rod−like divergent brachiophores, quadripartite muscle field and saccate mantle canal system. In both valves, posterior vascula terminalia markedly incurved posterolaterally, oblique to ribbing direction and intersecting posterior valve margin.

Discussion.—Externally and internally these large shells are very characteristic of the Orthidae , sharing with Orthambonites Pander, 1830 many of its diagnostic features. For example, the studied shells are very similar externally to Orthambonites fundata Rubel, 1961 among other species in the genus. Nevertheless, the attitude of its posterior vascula terminalia, oblique to the ribbing and intersecting the posterior valve margin, is a very peculiar feature within the orthids and is treated as a diagnostic feature of the new genus. Such a disposition of the vascula terminalia is known only within the family in Sinorthis typica Wang, 1955 , as in its Chinese specimens ( Zhan et al. 2006: pl. 3: 2) and in those from the Montage Noire, SE France (Mélou in Babin et al. 1982: pl. 3: 10–12). In any case, the taxonomic importance of this peculiar mantle canal system has not been evaluated up to now for the genus Sinorthis Wang, 1955 , which displays clear differences from the Iberian shells; among them, the ramicostellate ribbing and the divergent ventral vascula media, different detail of costate ribbing, and proximally parallel ventral vascula media in the new genus. The posterodorsally incurved vascula terminalia is a feature well known in some dalmanellidine orthides with markedly circular outlines, such as the Heterorthidae or the Drabovidae. Nevertheless it is very rare within the orthidine orthides. Curiously, such an incurved vascula terminalia is also known in Tarfaya Havlíček, 1971 , a genus assigned questionably to the family Heterorthidae (see Williams and Harper 2000; Villas and Herrera 2004; Benedetto 2007), but initially included among the Productorthidae ( Havlíček 1971) . Popov et al. (2009) have erected a new family Tarfayidae within the superfamily Orthoidea , including Tarfaya and Xinanorthis Xu et al., 1974 , characterised, among other features, by the posterolateral regions of dorsal valve with vascula terminalia along the hinge line.

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