Mitotic and meiotic chromosome preparations of Bellamya bengalensis f. doliaris (Viviparidae), Pi/a globosa (Pilidae) and Cyclophorus polynema (Cyclophoridae) were made by colchicine -ovotestis cell suspension -methanol acetic acid -flame drying -Giemsa technique. Karyotypes were prepared on the basis of decreasing length of the chromosomes and their morphometric analyses were done. The diploid number 2n = 22 with the chromosome formula n = 7m + 4 sm and FN = 44 forBellamya bengalensis f. doliaris, 2n = 28 with the chromosome formula n = 9m + 5sm and FN = 56 for Pi/a globosa and 2n = 28 with the chromosome formula n = 13m + 1sm and FN = 56 for Cyclophorus polynema were obtained. Chromosome numbers of each species was confirmed from the respective metaphase-! spreads and behaviour of their meiotic chromosomes were studied. The data obtained for each species were compared with the available chromosomal information on other confamilial species and the role of the possible mechanisms of karyotypic evolution in them have been discussed. Conservativeness with regard to chromosomal change at higher taxon levd has been discussed.

Two new genera, Brevishieldophyes Chakrabarti & Pandit, gen. n. and Mesoshieldophyes Chakrabarti & Pandit, gen. n., and a new species Mesoshieldophyesvarecae Chakrabarti & Pandit, sp. n. are described. These mites are leaf vagrants. The morphological characters of the afore-mentioned genera and those of Ashieldophyes Mohanasundaram are compared. A key for separating the genera within the subfamily Ashieldophyinae is provided. The diagnostic characters of the subfamily Ashieldophyinae are also revised.

Although study on the chromosomes of molluscs dates back from the last part of the 19th century, not more than 0.5% of the present day form of molluscs are known karyologically

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