30 linNj^ean arrangement. 



side is termed the rigid or outer lip (^pL 5. /. 60. c), and tlic 

 body of tlie shell, being in fact tlie outside of the preceding 

 whorl, is called the inner or pillar lip (]>/. 5. /. 60. rf) ; that 

 part of the aperture which is furthest from the spire, and called 

 by Linnaeus the base, in several genera ends in a canal or 

 hollow groove (^pl. 7. /. 88. a). M. Adanson calls this the 

 superior eanal \ sometimes there is a small hollow or notch 

 at the end of the mouth nearest to the spire (p/. 7. /. 91. a) ; 

 tliis M. Adanson calls the inferior canal. 



In many species, each whorl is joined to the preceding in 

 .such a manner that at the end opposite the spire they leave a 

 vacancy or hole in the centre, which sometimes extends to 

 the very point of the apex ; this aperture is called the umhilicua 

 (jpl. 8./. 98. a. and/. 105. o). Those shells that have this 

 umbilicus are said to be perforated, but in many species tlie 

 last whorl joins to or covers the former whorls in such a 

 manner as to leave no vacancy or hole ; these shells are called 

 imperforate ; there are a few species in which the young shelb 

 have an umbilicus, but as they get older they lose it, as Nerita 

 Maniilla. 



Most shells have a membrane or skin covering the outside ; 

 in some it is thick and rough, as though it were hairy, as in 

 some species of the Murex, Area, &c., particularly in Area 

 Note and barbata, and Mytilns Modiolus (p/. 4. /. 48. a) ; in 

 most it is very thin, and some are without any, as are all the 

 Cypi^cere, Voluta Oliva, and some species ofDonax : it is said by 

 Adanson to contribute to the growth and preservation of the 



