Beyrichiacean Ostracodes Associated with the Earliest Silurian Vertebrates from Gotland

Vertebrates older than any previously known from Scandinavia were recently found in the Halla Beds, the penultimate stratigraphical unit within the Wenlockian according to Hede (1942). The fauna, containing thelodonts, anaspids, and an osteostracan species, shows affinities to that in the Kaarma Beds of the Isle of Ösel (Saaremaa). This fauna is associated with a well preserved fauna of ostracodes of which the beyrichiaceans are described herein. They comprise one treposelline, Prisculella garnielloides, n.g., n.sp., and three beyrichiines, Beyrichia sp. (only tecnomorphs known), Beyrichia (Beyrichia) subornata Martinsson, and Calcaribeyrichia duplicicuspidata n.sp. The latter species is the earliest representative of a large, mainly Ludlovian group of species, and the entire fauna shows a more advanced aspect than that in the Mulde Beds which, according to current correlations, have been regarded as younger than the Halla Beds.