Keys to the families of the land and fresh-water snails of Texas.
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These keys cover families of the known land and fresh water snails of Texas. In land snails which produce external shells, the key is based upon only the mature shell. Such a treatment is necessary because, in the main, immature shells do not exhibit all of the characteristics present in the adult shells. The keys are based upon size and shape variations of the shell. Within one family shells of a variety of shapes may be found. Consequently, the differently shaped shells would not key to that family if the family name was mentioned only one time in the key. Major breaks or divisions in the key are based upon the more obvious differences such as height of shell greater than the diameter or the reverse, shell size, shell ornamentation, or whether the shell is glossy or dull. We have also included under each family the known range of the family in Texas. Where a single genus or species is keyed separately from the other members of a family, its range for the State is listed separately. It must be understood that the ranges for the separate species make up the total range for that family. Exceptions to this are certain families whose ranges are restricted to a particular section of the State.