140 INTRODUCTION TO CONCHOLOGY. 



One solitary species lias alone been acknowledged as per- 

 taining; to the c^enus Banldvia. The shell has few charac- 

 ters in common with Menchis, being apparently without an 

 epidermis ; but its porcellaneous structure resembles that 

 of the FhasianeUa, and it is sometimes banded with deep- 

 red and purplcj sometimes tastefully adorned with fine 

 zigzag lines. The columella presents the most important 

 generic feature, being thickly rolled and twisted, and trun- 

 cated at its junction with the lip, which is thin and not 

 reflected. 



The common periwdnkle, LiUorina mdgaris, presents a 

 famiHar type of the very natural group to which it per- 

 tains, including a multitude of species, of wdiich many are 

 yet undescribed. They dwell on rocks that line the shores, 

 but generally above the w^ater, although within reach of the 

 spray. Their general aspect, and the composition of their 

 shell, indicate that they belong to an animal dissimilar in 

 his habits from FhasianeUa ; and such is the fact, for the 

 molluscous inhabitant of the LiUorina has a more probos- 

 cis-like head, but without a fringed collar or finger-like 

 processes. 



The mention of the common periwinkle is associated with 

 the chffs of Tenby, where the shell-collector first saw a 



