Permian Orthotetoidea on Hydra belong to the genera Cyndalia Grant (19
93a), Goniarina Cooper and Grant (1969), Derbyia Waagen (1884), Diplan
us Stehli (1954), Schuchertella Girty (1904), Sicelia Merla (1934), an
d Tropidelasma Cooper and Grant (1969). Hydra has the most complete Pe
rmian section in the Western Tethys, 500 m thick and ranging in age fr
om Asselian to Dorashamian. These are the youngest silicified Permian
brachiopods west of China.