282 POPULAR BRITISH CONCHOLOGY. 



at various intervals : in some species regular^ in others irre- 

 gular. In Triton i\\Qj are rather irregular^ occurring at va- 

 rious parts of the whorls ; in Murex they are so regular as 

 to form uninterrupted ridges up the spire, by occurring in 

 the same position in each successive whorl : they are then 

 described as contimious. In Harpa and Scalaria they are 

 beautifully regular and smooth ; in Murex they are some- 

 times variously and beautifully fringed, or branched, or 

 spinous. 



RIDGES AND STRI^. 



All striae, or ridges, or furrows, or wrinkles, in the same 

 direction as the lines of growth or the varices, are described 

 as lo7igitudinal or concentric: all in the other direction, or 

 following the turns of the spire, are spiral. 



THE APERTURE, 



Or opening of the spiral hollow, is sometimes named the 

 mouth; but this is hardly suitable, because there would then 

 be the mouth of the shell and the mouth of the animal, 

 and, in describing the mollusc, great confusion might arise 

 between the two. The aperture is described as a whole, in- 

 cluding the columella, the outer lip, and any canals into 



