284 POPULAR BRITISH CONCHOLOGY. 



sometimes recurved, or turned back over the body of the 

 shell ; and sometimes it is varicose, forming a spiral ridge or 

 tumidit}^ In some of the Miirices it is closed by the meet- 

 ing of the edges, excepting at the very extremity ; in other 

 cases it is simple and open. 



The inyier or columellar lip of the aperture commences 

 when it joins the last or body-whorl, and is generally sepa- 

 rated at the lower end from the outer lip by the notch or 

 canal found in most species. The outer lip is measured 

 from where it joins the body-whorl above, to where it joins 

 the inner lip below. 



It may be remarked, that I am now using the words above 

 and lelow, upper and lower, because the shells are being 

 considered mathematically rather than naturally. Tor in 

 crawling, the head of the mollusc is projected from near 

 the lower part of the aperture, and the point or apex of the 

 shell would lie backwards ; so that some writers describe the 

 part of the aperture nearest the spire as posterior, and that 

 nearest where the head of the animal protrudes as anterior. 

 It is thus indeed that I have represented some of the mol- 

 lusca in the former part of this work. The outer lip, some- 

 times named the right lip, or lalrum, by continental writers, 

 is sometimes reflected, or turned outwards, and sometimes 



