THE SYSTEMATICS OF AMPHOROID DIATOMS - THE LIFE-HISTORY OF AMPHORA-ARCUS

Amphora Ehrenb. ex Kutz. is a large heterogeneous genus, which lacks a n adequate diagnosis and requires revision. Protoplast structure, plas tid division and sexual reproduction are described for Amphora arcus G reg. and used as a basis for a discussion of relationships within the genus. An apparently natural group can be distinguished within Amphora sensu lato, characterized by the presence of a single ventral plastid , rearrangement of the gametes within both gametangia before plasmogam y, morphological and physiological isogamy, and expansion of the auxos pores at right angles to the apical axes of the gametangia. The specie s belonging to this group are drawn from five of the nine subgenera re cognized in the classic account of Amphora by Cleve and include the ty pe species, A. ovalis (Kutz.) Kutz., as well as A. arcus. Some other A mphora species are not closely related to A. ovalis and A. arcus, and will need to be removed into new or resurrected genera. Cleve's subgen era are not themselves an adequate basis for revision, since most of t hem are heterogeneous. A lectotype is designated for A. arcus.