Notes on the squamation in psammosteids

Of the numerous psammosteids' (Agnatha, Heterostraci) only one species, Drepanaspis gemuendenensis Schlüter (Lower Devonian, Rhineland), shows an articulated squamation and а we,U-preserved caudal fin. Drepanaspis exhibits the three main kinds of scales characteristic of all psammosteids: flank scales, ridge scales and tail fin scales. Narrow overlapping margins of scales are also а noteworthy feature in psammosteids. In this paper, partly preserved squamation of the Middle Devonian Schizosteus striatus ( Gross) and Psammosteus sp. is demonstrated. The Psammosteus species differ from other psammosteids in possessing small and rather uniform scales. This type of squamation could hardly have Ьееn derived from that of Psammolepis and, consequently, Psammosteus was not а descendant of Psammolepis.