148 POPULAR BRITISH CONCHOLOGY. 



kind of squareness in the whorls ; it sometimes occurs 



with a beautiful tinge of bright purple in the aperture, 



under the bright golden edge of the outer lip. The 



animal is either a yellow or of a dusky tint, with the 



head and horns black. L. fahalis and L. palliata of 



authors are included. 



II. Lacuna receives its name from the hollow spiral 



groove behind the open spreading apertures of the shells 



which belong to it. The mollusc lives on seaweeds on the 



shores, like Littorina ; the foot is rounded at both ends, 



the front part being partly separated into a lobe; on the 



upper part of the foot is a lobe, or lappet, terminating in a 



filament at each hinder corner ; and on this lappet is fixed 



the operculum, w^hich resembles that of Littorina. The 



shells of this group are very pretty, and may be summarily 



described as follows : — 



L.joallidula, (including L.patula) : broad, smooth, with large 

 wide aperture, very small spire, a dull pale yellow epi- 

 dermis, and broad, white umbilical groove. 

 L. puteolus : globular, mouth not quite so large in propor- 

 tion to spire ; clearly banded with dark brown. 

 L. vincta : pyramidal, oval, with a produced spire ; smooth, 

 sometimes banded. 



