Mr. Robert Gamer's Malacological Notes. 371 



bonnet." A similar formation, but less gradual and more 

 anterior, produces such shells as Xavt'cella, already dwelt upon ; 

 whilst, if the mantle expands laterally instead of totally in 

 front, we have the corresponding form of the river and lake 

 Anci/luSj or of the internal shells of Aplysia^ Limax^ and 

 Bullcea. If the lower or iimer part of the mantle does not 

 secrete at all, the spiral shell can have no labium or inner lip, 

 and no inward pillar or columella, the axis of rotation. In 

 iScalan'a, but for the opposite reason, the shell has no material 

 axis, there being an approach to the disjoined Vermetus. The 

 shape of a transverse section of the spiral tube of a shell (that 

 of the angular-edged Trochus for instance, or of the rounded 

 Turbo) is due to the shape of the bend in the edge of the 

 mantle. The oblique direction of the mouth of a shell, and 

 consequently the produced spire, are owing, as alluded to 

 before, to the extra development of the component right valve. 

 A rotation on the same plane (as seen in the Xautilus and 

 sometimes in Planorbis) and the slow or rapid increase in the 

 diameter of the whorls occasion the preceding ones to be 

 apparent {A mmom'fen) or coyeved-'in {Bellerojj/ion). In Conus 

 the mantle-opening is disposed in the opposite direction to 

 what is most usual, and still more so in Ovula or Cyprceaj 

 being in the same line as the foot, and not transverse or 

 diagonal to it ; and the consequence is, that the last whorl 

 more or less covers up the spire of the shell, which, however, in 

 some cases, appears to become absorbed. In Chiton the 

 valves, except the last, answer to the anterior part of the shell 

 of a Patella or llipponyx^ in some species of which there is 

 a tendency for the successive laminae to separate. The shell- 

 umbo appears to be the middle of the last valve in Chiton. 

 There is also in Chiton as in Xerita some tendency of the 

 pedal nerves to put on the disposition seen in Articulata ; and 

 the auricles communicate with the elongated ventricle by two 

 or three openings on each side {Chitonellus) . The intestine 

 has been described to go in a straight line from head to vent, 

 but is in reality, in some species, more convoluted than in any 

 other mollusk*. 



The shell of the Nautilus and also of the Argonaut appear 

 to correspond in external form, and excepting the multilocular 

 character of the former, to those of the spiral Gastropods, 

 though, from the symmetrical disposition of the animals, and 

 the restoration of the branchiae to their original bilateral and 



* Perhaps the truest approach in a molluscan to the Articulata is in 

 several teclibranchiate species, as Alcera buUata, where the posterior somite 

 of the body is so distinct as to have its separate pair ot ganglia, irre- 

 spective of those for the supply of the vital organs. 



