HETERODEIDAE JAEKEL 1903

Zhu, You-An, Zhu, Min & Wang, Jun-Qing, 2016, Redescription of Yinostius major (Arthrodira: Heterostiidae) from the Lower Devonian of China, and the interrelationships of Brachythoraci, Zoological Journal of the Linnean Society 176 (4), pp. 806-834 : 809

FAMILY HETERODEIDAE JAEKEL 1903

Type genus: Heterostius Asmuss, 1856 .

Diagnosis: Moderately to very large arthrodires with the cranial and trunk shields broad and dorsoventrally compressed. The skull roof narrows anteriorly, and the posterolateral corners of the skull roof are in line with the posterior margin. The orbits are small, anterodorsally positioned. The dermal plates on the posterior part of the skull roof are moderately long, while those on the anterior part are short. The condyles of the cranio-thoracic joint are strongly developed, but not transversely elongated. The lateral wall of the thoracic armour are much reduced, the anteri- or lateral plate is fused with the anterior dorsolateral plate. The anteroventral part of the anterior lateral plate develops into an elongated, rod-like process. The ventral thoracic armour is reduced to a single plate that extends far anteriorly under the head.