The history of terrestrial and fresh-water gas tropods is interesting. The earliest form known is Pupa, found in the Devonian beds of Saint John, N. B., while a Pupa and a Zonites, remarkably close to the existing species, have been found in the coal measures of the Carboniferous. In the Mesozoic are found numerous finviatile genera, such as Planorbis, Melania, Hydrobia, Valvata, Physa, Limmea, Amnicola, and. Carychium. In the Cretaceous appear, in addition to those al ready cited in the Jurassic, Vivipara, Glandina, Bulimus, Goniobasis, Lioplax, Pleuroceras, and in the Tertiary deposits the land and fresh-water snails are quite as abundant as they are at the present time.
Some interesting evolutional series have been worked out among fossil gastropods. Neumayr has shown how Vivipara of the Miocene beds of Slavonia starts in the lower layers as smooth shells with rounded whorls, and changes, or evolves, through the succeeding overlying beds by successive intermediate stages into a more elevated shell, with concave whorls and nodose surfaces, that occurs only in the highest beds. Hilgendorf, and afterwards Hyatt, showed the peculiar transformations of Planorbis in the fresh-water Miocene beds of Steinheim, Wfirttem berg. Other similar evolutional series have been worked out for the Melaniidce, Cerithiidm, Volu tidm, MitridEe, and Turritellidm.
BIBLIOGRAPHY. For general information and Bibliography. For general information and anatomy, consult: Parker and Haswell, Text Book of Zoology, vol. i. (London and New York,
1897) ; Fischer, Manuel de conchyliologie et de paleontologie conchyliologique (Paris, 1897) ; Tryon and Pilsbry, Manual of Conchology (16 vols., Philadelphia, 1879-96) ; Pelseneer, Intro duction a l'etude des mollusques (Brussels, 1894) ; Lang, Text-Book of Comparative Anat omy, translated by Bernard, vol. ii. (London and New York, 1896), which contains an excellent bibliography of gastropod anatomy and physi ology; Walther, "Die Lebensweise der Meeres• thiere," in Einleitung in die Geologic, part ii. (Jena, 1893) ; Gould, Invertebrates of Massachu setts, edited by Binney (Boston, 1870). For fossil gastropods, see Von Zittel and Eastman, Text-Book of Paleontology, vol. i. (London and New York, 1900), where a good bibliography of fossil gastropods is given; see also Ulrich and Scofield, "The Lower Silurian Gastropoda of Minnesota," in Minnesota Geological and Natural History Survey, Paleontology, vol. iii., part ii. (Minneapolis, 1897) ; Lindstrom, "On the Silu rian Gastropods and Pteropods of Gotland," in Kongliga Svenska Vetenskaps-Akademiens Hand linger, vol. xix., No. 6 (Stockholm, 1884) ; and Dall, "Contributions to the Tertiary Fauna of Florida," in Transactions of the Wagner Free In stitute of Science, vols. iii. and iv. (Philadelphia, 1895-97). See articles on MOLLUSCA, and on the various families and genera of gastropods.