Several fragilarioid diatoms were found in surface sediment samples from Connecticut (U.S.A.) as part of a paleolimnological study on a set of 60 freshwater lakes. Observation of acid-digested material under scanning electron microscopy (SEM) revealed morphological variants of Staurosira and Stauroforma absent or seldom illustrated in the literature. Morphological variants of Staurosira reported here could be misidentified during routine ecological analyses due to limitations at the light microscopy (LM) level and because identification keys do not incorporate descriptions of such morphs. SEM observations also revealed the existence of two new fragilarioid taxa in 3 of the 60 Connecticut lakes. One of the new taxa is described here as Pseudostaurosira trainorii sp. nov. and appears to be distributed in fresh and brackish waters. For the second taxon, Pseudostaurosiropsis, nov. gen., is described based mainly on areolar and closing plate structure, features that are visible only at higher SEM magnifications. Pseudostaurosiropsis connecticutensis, sp. nov., with three freshwater populations in Connecticut, is the type species. Morphological aspects and ecology of the newly described taxa, as well as their relationship with other fragilarioid diatoms are discussed.

Genus et species novae: Pseudostaurosiropsis, gen. nov.; P. connecticutensis, sp. nov.; Pseudostaurosira trainorii, sp. nov.