Two Cyclotella species were found during the electron microscopic investigation of core samples from Lake La Cruz. Cyclotella distinguenda Hustedt was subdominant in the layers 80-110 cms and C. delicatula Hustedt was frequent and abundant in the layers 20-180 cms. SEM studies revealed an interesting variation in their valve structure elements. Analyses of the morphological characteristics of these species on the basis of SEM micrographs (55 photos were taken from C distinguenda and 95 from C. delicatula) was made it possible to complete their description. In this paper, the similarities and differences between Cyclotella distinguenda, C. delicatula and related taxa (Cyclotella azigzensis Flower, Gasse et Hhkansson, C costei Druart et Straub, C cyclopuncta HAkansson et Carter, C. granulata Kulumbaeva et Genkal, C. plitvicensis Hustedt, C wuethrichiana Druart et Straub) are discussed.