Achnanthes delicatula var. pacis Frenguelli, 1923 (original description)
Amphora libyca f. major Frenguelli, 1923 (original description)
Amphora libyca var. cymbiformis Frenguelli, 1923 (original description)
Amphora lybica f. major J.Frenguelli, 1923 (original description)
Amphora lybica var. cymbiformis J.Frenguelli, 1923 (original description)
Amphora perpusilla var. exilis (Grunow in Van Heurck) Frenguelli, 1923 accepted as Amphora pediculus var. exilis Grunow in Van Heurck, 1880 (new combination reference)
Anomoeoneis sculpta var. doliolus Frenguelli, 1923 (original description)
Anomoeoneis sculpta var. temperei (Frenguelli) Frenguelli, 1951 (original description)
Caloneis ventricosa var. elliptica Frenguelli, 1923 (original description)
Epithemia gibberula var. argentina (Brun in Brun & Tempère) Frenguelli, 1923 accepted as Epithemia argentina Brun in Brun & Tempère, 1889 (new combination reference)
Gomphonema augur var. capitulata Frenguelli, 1923 (original description)
Gomphonema clerici Frenguelli, 1923 (original description)
Gomphonema constrictum f. schmidtii Frenguelli, 1923 (original description)
Gomphonema constrictum var. schmidtii Frenguelli, 1923 accepted as Gomphonema constrictum Ehrenberg, 1832 accepted as Gomphonema truncatum Ehrenberg, 1832 (original description)
Gomphonema parvulum var. lagenula (Kützing) Frenguelli, 1923 accepted as Gomphonema lagenula var. lagenula Kützing, 1844 (new combination reference)
Navicula aperta Frenguelli, 1923 accepted as Pinnularia aperta var. aperta (Frenguelli) F.W. Mills, 1934 (original description)
Navicula bacterium Frenguelli, 1923 (original description)
Navicula clericii Frenguelli, 1923 accepted as Pinnularia Clericii (Frenguelli) Mills, 1934 (original description)
Navicula doeringii Frenguelli accepted as Pinnularia doeringii (Frenguelli) Mills, 1934 (original description)
Navicula doeringii var. doeringii Frenguelli, 1923 (original description)
Navicula gracilis f. constricta Frenguelli, 1923 (original description)
Navicula microstauron var. subproducta (Grunow in Van Heurck) Frenguelli, 1923 accepted as Navicula brebissonii var. subproducta Grunow in Van Heurck, 1880 (new combination reference)
Navicula ovalis var. oblongella (Nägeli) Dippel, 1905 accepted as Navicula oblongella var. oblongella Naegeli in Kutzing, 1849 (new combination reference)
Navicula peregrina var. curta Frenguelli, 1923 † (original description)
Navicula perrotetii var. rostrata Frenguelli, 1923 (original description)
Navicula pygmaea Frenguelli, 1923 (original description)
Navicula ventricosa var. elliptica Frenguelli, 1923 accepted as  (original description)
Navicula viridis var. distinguenda (Cleve) Frenguelli, 1923 † accepted as Pinnularia viridis var. distinguenda Cleve, 1891 † (new combination reference)
Nitzschia calica var. salinarum (Grunow in Cleve & Grunow) Frenguelli, 1923 accepted as Nitzschia tryblionella var. salinarum Grunow in Cleve & Grunow, 1880 (new combination reference)
Nitzschia laevis Frenguelli, 1923 (original description)
Nitzschia levis Frenguelli, 1923 (original description)
Nitzschia vitrioides Frenguelli, 1923 (original description)
Pinnularia Clericii (Frenguelli) Mills, 1934 (original description)
Rhopalodia gibberula var. argentina (Brun in Brun & Tempère) Frenguelli, 1923 accepted as Epithemia argentina Brun in Brun & Tempère, 1889 (new combination reference)