The highest male haploid chromosome number so far recorded in the Odonata is 19, Occurring in Argia apicalis and A. tibialis (B. K.IAUTA & M.A.J.E. K1AUTA, 1980, Odonalologica9:35- -36). No species with haploid chromosome number higher than n= 14 (¿J) has been reported in Anisoptera, though in Diplacodes bipunctata B. KIAUTA (1969, Genelica 40: 158-180) reported 12 bivalents, an X chromosome and 2 additional elements in 40% of the metaphase-1 cells studied. About the latter, however, "it is not clear whether or not they have a bivalent structure”. Most of the n=14 species are referable to Aeshnidae, and onlyafewtoLibellulidae(cf. B. KIAUTA, 1972, Odonalologica 2: 73-102; — 1979, Odonalologica 8: 267-283; A.M. DE SOUZA BUENO, 1982, Esludos cromossomicos na or den Odonala, M. Sc. thesis, Univ. Estat. Paulista, Rio Claro; S.K. SANGAL & B.K. TYAG1, 1982, Notul. odonatol. T. 154-155; A. STEINEN, 1982, Notul. odonatol. I: 167-168). Chromosome studies were carried out in 3 <5 of Orthemis nodiplaga (2 <5, Parque Pereyra Iraola, Provincia de Buenos Aires, Argentina; I i5, Palermo, Ciudad de Buenos Aires, Argentina). Staining and squashing were performed in 2% propionic haematoxylin with 1% ferric citrate as mordant. All the specimens were identified by Dr A. Rodrigues Capitulo and are kept in the Institute de Limnologia, Facultad de Ciencias Naturales y Museo. La Plata, Argentina, under the Collection Inventory Nos 1090, 1091 and 1092.