A study was undertaken of catfishes of the family Clariidae in Nyasaland, excluding that small part of the Shire River system which lies below the Murchison cataracts. Of fourteen species found, four, belonging to the genus Clarias, are not endemic and are found mainly in rivers, streams and swamps, inhabiting Lake Nyasa sparsely and only where similar conditions are found. The lake has been colonised mainly by the remaining ten species, which are all endemic to it, specialised for lacustrine conditions and sufficiently distinctive to warrant a new genus being proposed: genus Bathyclarias nov. The ten species of the genus form a species-flock, having a variety of habitats. Seven are new and are described and figured: Bathyclarias loweae, B. ilesi, B. rotundifrons, B. euryodon, B. filicibarbis, B. worthingtoni and B. gigas, spp. n. Notes on distribution and ecology are given in all cases, and a key is given for all members of the family in Nyasaland.