Psammosteiformes (Agnatha) - A review with descriptions of new material from the Lower Devonian of Poland. 2. Systematic part

The present work consists of the second part of a comprehensive review of the order Psammosteiformes - a group of the subclass Heterostraci (one of the major divisions of the Agnatha, or jawless vertebrates). Part I (General) of this review, which is published as a separate volume - Palaeontologia Polonica No. 13 - contains an introduction to the Heterostraci as a whole, including a new interpretationof their internal anatomy, as well as sections on the following topics which relate exclusively to the psammo steids: an historic al review of previous work; an account of the morphology of the psammosteids together with a discussion of their classification; an account of the growth of the dermal armour based on a detailed examination of its ornamentation ; a re-interpretation of the histology of the aspidin and dentine of the dermal armour with particular reference to their fine structure; an account of the stratigraphical range and geographical distribution of the group, and finally a discussion on the origin and evolution of the psammosteids. This work - Part II (Systematic), contains full descriptions of, and comments on, all available psammosteid material, while in addition problems relating to morphology or evolution are discussed when they pertain to particular specimens. Although much of the material is described here for the first time, previously described material has also been re-examined, enabling a comprehensive critical assessment to be made of the entire order. As can be seen from the List of Contents, the descriptions have been compiled in a systematic way based on the classification discussed in detail in Part I, and outlined briefly in my paper on the Classification and Evolution of the Heterostraci (1 962c). In consequence of the publication of this review in two distinct parts, an Appendix was included at the end of Part I so that all new taxa could be validated , thus preventing their remaining nomina nuda until this Part IT appeared.