that is to say the amount of longitudinal shearing, or displacement parallel to the axis of the shell.
The enveloping angle, or rather semi-angle (ö¡), of the cone may be taken as 90ô¯ in the discoid shells, such as Nautilus and Planorbis. It is still a large angle, of 70ô¯ or 75ô¯, in Conus or in Cymba, somewhat less in Cassis, Harpa, Dolium or Natica; it is about 50ô¯ to 55ô¯ in the various species of Solarium, about