Atlantic Continental Shelf and Slope of the United States - Ostracode zoogeography in the southern Nova Scotian and northern Virginian faunal provinces

Ostracodes were identified from 236 bottom samples taken in the region from Nova Scotia to Long Island. There is a distinctive difference between the assemblages in the northern and southern parts of this region. Many sublittoral cryophilic species are not present south of Cape Cod or the Northeast Channel, and several thermophilic species a.re not .found north of Cape Cod or Georges Bank. The ostracode assemblages in the southern part of the cold-temperate Nova Scotian province are a mixture of amphiatlantic cryophilic species and endemic, mainly thermophilic species; European forms make up approximately 50 percent of the species. Less than 25 percent of the species known from the mild-temperate Virginian province have been reported from European waters. More endemic species pass Cape Cod from the south than amphiatlantic cryophilic species do from the north. This is consistent with the fact that summer isotherms are more compressed than winter isotherms in the Cape Cod region, and the southern limit of distribution of most amphiatlantic species is regulated by summer high temperatures. The distribution data on which these interpretations are based are presented in a series of .figures and over 60 species distribution maps.