Eine Abhandlung über die malakologie; oder, Muscheln und Schalentiere. elidomus. Im Hinblick toits Affinität, Wir vermuten, dass es füllt den gleichen situationamong der Rotellince die Onustus wird unter theTrochintp: Dadurch wird es den meisten aberrante Typ, andconsequently, kommt in der Nähe des HelicidfB, dessen Form sie tatsächlich besitzt. Die beigefügten Zahlen {Abb. 41.) sind von der nur twospecimens in unserem Schrank, die wir haveeither gesehen oder gehört; die Linie denotestheir natürliche Größe genommen. Somit gibt Es groundfor, angenommen, dass der Übergang von themarine TrochidcB zu den terrestrischen snailsis durch o gekennzeichnet

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A treatise on malacology; or, Shells and shell fish . elidomus. In regard toits affinity, we suspect that it fills the same situationamong the Rotellince which Onustus does among theTrochintp : this will make it the most aberrant type, andconsequently that which comes nearest to the HelicidfB, whose form it actually possesses. The annexed figures{fig. 41.) are taken from the only twospecimens in our cabinet which we haveeither seen or heard of; the line denotestheir natural size. Thus, there is groundfor supposing that the passage from themarine TrochidcB to the terrestrial snailsis marked by one or more fluviatile types, just as is the passage on the other side ofthe Helicidcp, marked by the Limnacince. The accidentaldiscovery, also, of this extraordinary shell, will probablyinduce naturalists to a more accurate examination of thefossil turbinated univalves than they have received , • forit is clear, that, although Thelidomus opens the path tothe Helicidce, there must be several other forms betweenthe two, either extinct or undiscovered.. CHAP. VIII. THE PHYTOPHAGOUS GASTROPODS CONCLUDED. THE HALIOTIDj«, OR EAR-SHELLS, AND THE NA71CID^, OR NERITS. (213.) The Haliotid.^, or ear-shells, follow theTrochidfE, and, like them, in their typical examples, areof a rich pearly and iridescent substance. They have CHAP. VIII. haliotida: generally. 229 been confounded, even by Cuvier, with the true Scuti-branchia, merely because, like them and the Tuhuli-branchia, their mode of generation is the same. If thislatter consideration is of such importance, all these threeshould form one group; and not only so, but they shouldbe united to the Dythera, or bivalves, — since they also arefecundated in a similar manner. The fact, however, appears to come out, by analysis, that the Haliotidcs arethe representatives of the limpets (^Scutihranchia) in thegreat circle of the phytophagous gastropods, just as thenaked dorises (Nlidibranchia) represent the limpets(^Scutihrancliia) in the entire

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• bookcentury1800
• bookdecade1840
• booksubjectmollusks
• buchjahr184