XII.—Notes on the Genus Corvaspis

Recently discovered fragments of the armour of the ostracoderm Corvaspis are described, together with similar material from Vestspitsbergen and Podolia. The fossils have been obtained from Lower Old Red Sandstone deposits of Upper Downtonian–Lower Dittonian age. Large, thick, median plates, small irregular plates, orbital and ridge plates, and small, thick polygonal scales are present amongst the material. The characteristic external ornamentation of smooth, narrow ribs of dentine and a marginal band of small, smooth irregular tubercles is present on all plates. Two species are distinguished by their slightly differing ornamentation: Corvaspis kingi is known from the three regions named, C. graticulata sp. nov. comes from somewhat higher in the Vestspitsbergen sequence, and bears a finer ornamentation. A new family of heterostracans is erected to contain the genus, which in general structure may have been somewhat akin to the Drepanaspidæ, although no complete reconstruction can yet be attempted.