Abstract
Amphora species collected from British rivers and lakes have been studied by scanning electron microscopy. The original aim was to check on the distribution of the three widely reported species (A.ovalis, A.ovalis var. affinis and A.pediculus) in rivers and lakes and determine any variation in morphology. In the event numerous forms of each species were discovered and this paper deals with those of Amphora ovalis. The existence of morphological forms (phenodemes) in diatoms is discussed briefly. Amphora valves are asymmetric and the terminology of the various parts are discussed in relation to terms used by earlier workers. The type of A.ovalis and four other forms of A.ovalis have been photographed in the SEM and these are briefly described. The forms have been designated A-D and not given names.