Nine species of the ostracod genus Sclerochilus which live in British waters are diagnosed and illustrated, including lour new species: S. hicksi, S. rudjakovi, S. schornikovi, and S. whatleyi. The appendages of the genotype, S. contortus, are illustrated for the first time, and many previous records of that species are shown to be erroneous. A pictorial key is provided to facilitate identification.