A treatise on malacology; or, Shells and shell fish . ^;- ^]Melanella. Pla.axis. I The use of the last, or additional column, which con-tains the genera of the entire sub-family, is chieflyfor the purpose of showing that Melatoma, while itpreserves its analogy to Pleurotoma, agrees also withPlanaxis in having the base notched, and with Mela-nella by its thickened inner lip. (187.) The next genus is that of Cerithidea. Wehave now come to the cyclostiform type, which, withthe elongate form of Scalaria, has an effuse and circularaperture, with the outer lip dilated into a broad fringe,and a very
![A treatise on malacology; or, Shells and shell fish . ^;- ^]Melanella. Pla.axis. I The use of the last, or additional column, which con-tains the genera of the entire sub-family, is chieflyfor the purpose of showing that Melatoma, while itpreserves its analogy to Pleurotoma, agrees also withPlanaxis in having the base notched, and with Mela-nella by its thickened inner lip. (187.) The next genus is that of Cerithidea. Wehave now come to the cyclostiform type, which, withthe elongate form of Scalaria, has an effuse and circularaperture, with the outer lip dilated into a broad fringe,and a very Stock Photo](https://c8.alamy.com/comp/2AKM15B/a-treatise-on-malacology-or-shells-and-shell-fish-melanella-plaaxis-i-the-use-of-the-last-or-additional-column-which-con-tains-the-genera-of-the-entire-sub-family-is-chieflyfor-the-purpose-of-showing-that-melatoma-while-itpreserves-its-analogy-to-pleurotoma-agrees-also-withplanaxis-in-having-the-base-notched-and-with-mela-nella-by-its-thickened-inner-lip-187-the-next-genus-is-that-of-cerithidea-wehave-now-come-to-the-cyclostiform-type-which-withthe-elongate-form-of-scalaria-has-an-effuse-and-circularaperture-with-the-outer-lip-dilated-into-a-broad-fringeand-a-very-2AKM15B.jpg)
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A treatise on malacology; or, Shells and shell fish . ^;- ^]Melanella. Pla.axis. I The use of the last, or additional column, which con-tains the genera of the entire sub-family, is chieflyfor the purpose of showing that Melatoma, while itpreserves its analogy to Pleurotoma, agrees also withPlanaxis in having the base notched, and with Mela-nella by its thickened inner lip. (187.) The next genus is that of Cerithidea. Wehave now come to the cyclostiform type, which, withthe elongate form of Scalaria, has an effuse and circularaperture, with the outer lip dilated into a broad fringe, and a very short notch at the base. The lightness ofthese shells would seem to indicate that they were flu-viatile ; but as they are slightly variegated, and haveno epidermis, we should not be surprised at their beingfound in the sea, —more particularly as this appears tobe the point where the series of fluviatile Testaceaterminates, and the marine commences. Nevertheless, the great change from Melanopsis to Cerithidea is not 204 SHELLS AND SHELL-FISH. PART I.. sudden; for it is here we shall insert, as an interveningform, our sub-genus Ceriphasia {fig. 38.), founded upon certain Ohio shells resembling Ce-rithidea, but whose outer lip is thinand sharp. Unfortunately, we canfind no account of the animal, norare we acquainted with any shellswhich wiU connect these with 3Ie-lanopsis on one side, and. with Ce-rithidea on the other. Until ourpath, therefore, is better marked, we must leave their precise situation as doubtful.There are evidently three or four sub-genera un-discovered or uncharacterised, which belong to thisgenus. One of these, we suspect, will be found incertain small species, figured as Melanopsides byM. Ferussac: their spire is unusually lengthened;and the whorls are strongly and longitudinally plaited.As our last genus, we introduce Plancijcis, —the animalof which, having been fully investigated and de-scribed by M. Quoy, proves that their shell must bearranged with the Mela