EXPLANATION OF PLATI VI. 



ia \ 



Fig. I. — Teeth of radula of Vitrea alliaria 

 -Teeth of radula of V. rogersi 

 . — Teeth of radula of V. helvetica J 



-Median vertical section of shell of Vitrea ce 

 -Median vertical section of V. rogersi. 



6. — Median vertical section of V. alliaria. 



7. — Median vertical section of V. nitidula. 



These four sections (prepared for me by Mr. Riu 

 the Mineralogical Department of the Natural History 

 shape of the whorls in transverse section, their relative 

 to the axis of the shell, the absence of real channellioL' 

 appearance of which in V. cellaria and V. rogersi as 

 alliaria and V. tiitidula is accounted for by the high 

 each whorl meets its predecessor. 



Figs. 4-7 are all drawn to the same scale, whir 

 10 mm. line placed close to them. 



8-10. — Vitrea helvetica. 



I r - 1 3. — V. rogersi. 



14-16. — V. alliaria. 



Figs. 8-16 are all drawn to the same scale, which 

 10 mm. line between them. 



the Lapidary in 

 ^eum) shew the 



iion in relation 

 '. ihe suture, the 

 :;rasted with V. 



ingle at which 



^ shewn by the 



dicated by the 



