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Abstract
Two new species of Fragilariforma, F. cassieae sp. nov. and F. rakiuriensis sp. nov., are described from material from New Zealand, with reference to populations found in Australia. The new species are similar in shape and size to Fragilariforma lata and F. hungarica var. tumida but are separated on the basis of areola and stria density, and shape. The distinguishing features of F. cassieae are a rhombic shape with narrow protracted ends, and striae with prominent areolae. In F. rakiuriensis, small forms are similar in shape to F. cassieae, but larger cells are elongated with a constriction at the centre. The striae are more widely spaced than in F. cassieae with a slightly irregular appearance and fine, closely spaced areolae. We discuss the relationships of the new species within the genus Fragilariforma, and also discuss the possible existence of further related taxa in the material examined, or marked shifts in form in their morphological progression during cell division. The two species described represent further evidence of a higher degree of endemism in Southern Hemisphere freshwater diatoms, and particularly in New Zealand and Australia, than has previously been assumed.