Achnanthes delicatula var. magellanica Frenguelli, 1924 (original description)
Actinoptychus undulatus f. quaternata Frenguelli, 1924 (original description)
Actinoptychus undulatus f. ternata Frenguelli, 1924 (original description)
Epithemia zebra var. zebra Frenguelli, 1924 (original description)
Eunotia praerupta f. inflata (Grunow) J.Frenguelli, 1924 (new combination reference)
Fragilaria construens var. minor Frenguelli, 1924 (original description)
Fragilaria construens var. tetragona Frenguelli, 1924 (original description)
Fragilaria pinnata f. brevistriata Frenguelli, 1924 (original description)
Fragilaria pinnata f. minor Frenguelli, 1924 (original description)
Fragilaria pinnata f. opephoroides Frenguelli, 1924 (original description)
Fragilaria pinnata var. tetragona Frenguelli, 1924 (original description)
Fragilaria virescens f. major Frenguelli, 1924 (original description)
Melosira laevis var. fuegiana Frenguelli, 1924 (original description)
Melosira sulcata f. crenulata (Grunow) Frenguelli, 1924 accepted as Paralia sulcata f. crenulata Grunow, 1884 (new combination reference)
Navicula divergens var. parallela (Brun) Frenguelli, 1924 † accepted as Pinnularia parallela var. parallela Brun, 1895 (new combination reference)
Navicula doellojuradoi Frenguelli, 1924 (original description)
Navicula lata var. latestriata (Gregory) Frenguelli, 1924 accepted as Pinnularia latistriata var. latistriata Gregory, 1854 (new combination reference)
Navicula peragalli var. gracilis Frenguelli, 1923 (original description)
Navicula peragalli var. peragalli Frenguelli, 1924 (original description)
Navicula viridis var. lata Frenguelli, 1924 (original description)
Navicula viridis var. transversa (A.Schmidt) Frenguelli, 1924 accepted as Navicula transversa A.Schmidt, 1876 (new combination reference)
Nitzschia panduriformis var. parva Frenguelli, 1924 (original description)
Surirella tuberosa f. elongata Frenguelli, 1924 (original description)