. Annual report - Western Society of Malacologists. Mollusks; Mollusks. The color, shape of the shells, morphology of the soft parts and the radula are some reference points on which the systematics are based (Inaba, 1965); the interrelation- ship between environmental geographic barriers, age of the organisms and other factors characterize the spteciation, adaptation and selection between populations (Inaba, 1965, and Burch, 1960). More exact techniques are required to help us in the description, identification and localization of species and subspecies. Pain, 1964, says that the genus Pomace
. Annual report - Western Society of Malacologists. Mollusks; Mollusks. The color, shape of the shells, morphology of the soft parts and the radula are some reference points on which the systematics are based (Inaba, 1965); the interrelation- ship between environmental geographic barriers, age of the organisms and other factors characterize the spteciation, adaptation and selection between populations (Inaba, 1965, and Burch, 1960). More exact techniques are required to help us in the description, identification and localization of species and subspecies. Pain, 1964, says that the genus Pomacea is found distributed in the southeast of Mexico as far as Belize and Guatemala, represented by P. flagellata The object of the present work is to establish a kary- ological analysis of the genus Pomacea from southeast Figure 1. Embryos of Pomacea flagellata. Materials and methods The chromosome number in each mitotic field was counted and the chromosomes were placed in homologous pairs according to the size of the chromatids and the posi- tion of the centromer. The karyotypes were measured using a constant mag- nification and the analysis was made according to the fol- lowing terms: p = short arm of the chromosome q= long arm of the chromosome Relative Length (R:L:) = percentage of all chromo- somes p/q + q centromeric index (C:l) = percentage of the short arm, over 1 total length of chromo- some arm ratio or proportion of short arms with short or long difference. Results The karyological characterization of the species (Figures 2-4) showed a fundamental number of 52 with a chromo- somic formula: 4M + 5m + 4 Sm (9 metacentric pairs; 4 submetacentric pairs), which 2n = 26 in the diploid phase, where it was inferred an- 13, observed they are bir- ramean. The karyological characterization of the species (Table 1) was made considering the chromosome classification system proposed by Levan & Sandberg (1964). Sex chromosomes were not identified. The representative ideo
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