Based on light and electron microscopical investigations, a new genus Craspedostauros is described for a group of marine biraphid diatoms previously placed in Stauroneis Ehrenberg. The genus Stauronella Mereschkowsky had been erected for one of these species, Amphiprora constricta sensu W. Smith, but Mereschkowsky's name cannot be used for nomenclatural reasons. Craspedostauros species can be recognized by the possession of cribrate areolae, a stauros that is usually narrower than the fascia, many girdle bands with double rows of cribrate areolae and two chloroplasts, fore and aft of the central cytoplasm, each with a central pyrenoid. The genus shows similarities in its pore structure and chloroplast type and arrangement to Mastogloia Thwaites ex W. Smith and Aneumastus Mann & Stickle, suggesting that it is more closely related to these than to other naviculoid genera with a stauros, i.e. Stauroneis, Staurophora Mereschkowsky, Meuniera Silva and Haslea Simonsen. The stauros is a feature that probably arose a number of times. A description of the genus and its currently recognized members is given, with a key to their identification. Four new species are described, the types of which have been deposited in the Natural History Museum, London. The status of Stauronella constricta var. linearis Mereschkowsky remains unclear in the absence of any material from the Black Sea. Some marine stauroneid diatoms that do not belong in Craspedostauros are briefly discussed.