. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. BASCII : FRESHWATER LIMPET SNAILS 441 habitat. Tlie specimens I have dissected, mostly from Michigan, have been heavily pigmented. The radnla is about the same as that of F. rivularis. Rcmorl-s: The large size, characteristically elongated sliell shape, lentic habitat, and restricted distribution distinguish this species from other Ferrissia, and I believe it to be a distinct, though variable, species. It appears to be a direct descendant of 7^. Fig. 19. Ferrissia parallela, tvpicnl specimens. Howe Lake, O
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. BASCII : FRESHWATER LIMPET SNAILS 441 habitat. Tlie specimens I have dissected, mostly from Michigan, have been heavily pigmented. The radnla is about the same as that of F. rivularis. Rcmorl-s: The large size, characteristically elongated sliell shape, lentic habitat, and restricted distribution distinguish this species from other Ferrissia, and I believe it to be a distinct, though variable, species. It appears to be a direct descendant of 7^. Fig. 19. Ferrissia parallela, tvpicnl specimens. Howe Lake, Ontonngon County, Michigan. DISCUSSION Ecology As an aid to understanding the phylogenetic relationships of anc^did snails, it is important that the ecology of these animals should be studied in some detail. Although much work of this kind has been done with the two European species and very little with the American forms, it is still of interest to review the ecological observations made upon the family and to try to apply these observations in the interpretation of American species. In this section an attempt will be made to isolate and discuss those elements of the environment which seem most important to ancylid snails. It is realized that an animal responds to its total environment, all of whose elements are bound together in a com- plex way; a change in one may induce changes in many others. Nevertheless, some physical-chemical and biotic factors have been singled out for special discussion below. Physical-chemical factors: Any given species of ancylid is normally to be found onl^^ in still water (lentic type) or running. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. : The Museum
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