Kloedenia and Related Ostracode Genera in the Silurian and Devonian of the Baltic Area and Britain

Submerged parts of the youngest Silurian sequence in the Gotland area, corresponding beds in Scania, and the lowermost Devonian beds in the Welsh Borderland contain a series of ostracode species more or less closely related to Kloedenia wilckensiana (Jones 1855). Species included in this taxion and in K. kiesowi (Krause 1891) are referred to the new genera Frostiella and Londinia with two species each (see Contents). In the genus Kloedenia, as restricted herein, no adult tecnomorphs have been found. The heteromorphic characters are acquired during the last moulting, but intermediate specimens are not uncommon, in contrast to conditions in all other Beyrichiacea. The slight cruminal metamorphosis in Kloedenia is the extreme, orthogenetic, opposite to the complicated palingenetic metamorphosis in Craspedobolbina; in Kloedenia only a simple inflation takes place along the strongly reduced velar fold, and the striate swelling along the velar edge is divided into three ridges. With the publication of the present study, the carapace morphology and the systematically important cruminal ontogeny of all major beyrichiacean groups, except the Zygobolbinae, have been treated on the basis of a representative material. The Beyrichiacea are subdivided in to two families, Craspedobolbinidae and Beyrichiidae, representing two developmental branches in velar morphology and cruminal metamorphosis. The main features in the beyrichiacean system are discussed. The study is largely based on new collections of erratic Beyrichienkalk ("Beyrichia Limestone") from Fornerania and Rtigen. The occurrence of these erratics and their geographical and stratigraphical origin are briefly discussed