20 LjNNiEAN ARRANGEMENT. 



side is termed the rigJit or outer lip (/)/. 5. /. 60. c), and the 

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

 whorl, is called the inner or pillar lip (/»/. 5. /. 60. d) ; 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 (p/. 7. /. 88. «). M. Adanson calls tliis the 

 superior canal ; sometimes there is a small hollow or notch 

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

 this 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 umbilicus 

 (^pl. 8./. 98. a. and/. 105. a). Those shells that have this 

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

 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 shells 

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

 Mamilla. 



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 Mytilus Modiolus (^pl. 4. /. 48. a) ; in 

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

 CyprfEte, Valuta Oliva, and some species of Donax: it is said by 

 Adanson to contribute to the growth and preservation of the 



