| An ecological study on the Korgass population of the land snail Cathaica cavimargo (Martens, 1879) was carried out. The study consisted of three parts: population distribution, shell biometric characters and shell colouration.The study sites were located in Kaying Bulakn, a valley situated at Mount Pokinur, 10 km northeast of the Talki livestock farm. The study covered an area of about 1 square kilometer, in which eleven sites were investigated. The populations of Cathaica cavimargo are distributed in a number of heterogeneous habitats, from the hillside to the valley. These populations (more precisely, subpopulations) have pronounced variations in population density, shell biometric characters and shell colouration.An analysis of population distribution took place on all of the 11 sites, and population size and density of 8 sites out of these 11 sites were estimated by direct counting method, in order to get basic information of the population ecology of Cathaica cavimargo. The area per site was 36 m2.The results indicated that there is a direct correlation between the distribution of the species and the distribution of stones. The sites with much limestone or granite have the highest population density. On the other hand, the sites with no stone, id est pure grass and pure shrubbery, had no distribution of Cathaica cavimargo. Only a single empty shell was found on the site of pure grass. Considering the distribution of the species, the sizes and grounding patterns of stone are of critical importance, but the kinds of stone haven't any significance.The shell biometric study employed a factor analysis. For the sake of accuracy, only sites having at least 20 specimens were considered; therefore the sites No.4, No.7, No.9 and No. 10 were excluded. The results of factor analysis showed that the following three shell factors are independent, and that there are no correlations among them: shell size, shell flatness and protoconch whorl number.In addition, to these three characteristics, there are also two other shell characters, shell thickness and shell smoothness, which are not easily studied by quantitative analysis.Snails living among boulders in open, sunlit habitats, are often large, and have sturdy, somewhat coarse shells; On the other hand, snails living on rock surfaces and in shaded hillside habitats have small, thin, very fragile and smoother shells. The distributions of shell flatness and protoconch whorl number are random, we could not find any notable distinction in the shell flatness of snails on surfaces of different inclinations.In a later process, using the three shell factors performed a hierarchical cluster analysis. Seven populations of Cathaica cavimargo were separated into two groups, one containing large-shelled populations in open sunlit habitats with many boulders. The other contained small-shelled populations in shaded hillside habitats and on rock surfaces. This process revealed strong correlation between the variation of shell biometric characters and the microenvironment.Shell colouration polymorphism in nine populations of the land snail Cathaica cavimargo living in different microenvironments, on 11 sites, was investigated. Shell colour varied from ivory white to deep brown. Some individuals had white banding right on the carina of their shells.Colour comparison were made by using a 'shell colouration index', which indicated the darkness of shells. There was large interpopulation and intrapopulation variation in shell colour. In general, the distribution of the shell colours was not completely random. Populations living in shaded places, characterized as dim and humid, had a high frequency of dark shells, while populations living in sunny and relatively dry, open places had lighter shells.We also considered the possible effects of humidity, temperature and altitude on population distribution, shell biometric characters and shell colouration, but we couldn't see any of their significance in the result. That was because, possibly: as regards humidity and tem...
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