THE OSTRACOD GENUS KRITHE FROM THE TERTIARY AND QUATERNARY OF THE NORTH-ATLANTIC

The ostracod genus Krithe is investigated from Cainozoic deep water se diments of the North Atlantic region, mostly from ODP/DSDP cores, alth ough other material is from short cores collected by various NATO vess els, and the geographical and stratigraphical occurrence of the princi pal species is detailed. The morphological features of the genus are d escribed, and their relative utility in specific discrimination assess ed. Of the seventeen species and subspecies described herein, eight ha ve been previously described, five species (Krithe gobanensis, K. regu lare, K. minima, K. aquilonia, K. praemorkhoveni) and two subspecies ( K. morkhoveni lamellalata, K. morkhoveni ayressi) are new, while two a re compared to previously described species. In addition, the stratigr aphical ranges and distribution of nineteen nomina nuda species, too r are to be formally described, are tabulated. A new system, based on th e nature of the anterior radial pore canals, is used to erect distinct species groups of the genus and as an aid in species determination. T he various carapace biocharacters of the genus are reviewed and evalua ted with respect to their taxonomic significance; many are shown to be of little use since they are very conservative within Krithe while ot hers, such as size, shape, degree of dimorphism and the nature of the anterior radial pore canals are shown to be of great importance. The s tratigraphical ranges of all known Krithe species in the North Atlanti c are given and the considerable biostratigraphical significance of th e genus is demonstrated. The previous use of Krithe in palaeoenvironme ntal reconstruction is discussed and the supposed relationship between vestibulum morphology and oxygen level critically evaluated and shown to be wanting, as is the proposition that there is a determinable rel ationship between the length of species of the genus and water depth.