Four new species of the genus Lacustriella (Bacillariophyta) from Lake Baikal

We add four new species to the recently established genus Lacustriella Kulikovskiy, Lange-Bertalot et Metzeltin and characterize morphology of the taxa based on LM and SEM observations. Lacustriella cuspi-data, L. rombea, L. radiata and L. solita share all of the typical morphological features of the genus including longitudinal canal along each valve margin, radiate uniseriate striae terminated with large elongated areolae, and external distant raphe ends bent oppositely. L. cuspidata is peculiar among the other Lacustriella with rows of small pores look as if they continue striae on the surface of longitudinal canals as well as with the axial area sharply widened into the asymmetrical central area. L. rombea is different in combination of valve outline with unprotracted rostrate apices, irregular areolation at centre of the external valve, and slit-like areola occluded with volae. In L. radiata distinctive characters include protracted rostrate valve apices, rhombic central area and volated slit-like areolae. L. solita differs in the highest density of areolae in striae and an ornamented surface of longitudinal canals. New species were compared to the closest morphologically similar taxa. Some general ecological properties and distribution in the littoral zone of the ancient lake are given.