﻿Analysis 
  of 
  a 
  certain 
  Group 
  of 
  Species 
  of 
  Cyclostoma. 
  57 
  

  

  ent 
  year 
  Mr. 
  Sowerby 
  has 
  described 
  a 
  third 
  type 
  under 
  the 
  

   name 
  of 
  C. 
  subn/gosum, 
  (Thes. 
  Conch. 
  II. 
  p. 
  IGl*, 
  pi. 
  Suppl. 
  

   31 
  B. 
  f. 
  308, 
  309.) 
  

  

  Having 
  found 
  some 
  difficulty 
  in 
  identifying 
  these 
  species, 
  

   I 
  concluded 
  first 
  to 
  study 
  the 
  shells 
  themselves 
  and 
  their 
  oper- 
  

   cular 
  which 
  are 
  in 
  my 
  collection. 
  Twenty 
  types, 
  which 
  have 
  

   seemed 
  worthy 
  of 
  notice, 
  are 
  described 
  below. 
  Perhaps 
  two 
  

   or 
  three 
  of 
  these 
  may 
  be 
  due 
  to 
  accident 
  or 
  circumstances 
  ; 
  

   but 
  most 
  of 
  them 
  are 
  probably 
  original 
  types. 
  Many 
  of 
  them 
  

   are 
  local. 
  For 
  the 
  most 
  part 
  they 
  are 
  of 
  less 
  value 
  than 
  is 
  

   usually 
  assumed 
  for 
  a 
  species. 
  

  

  A. 
  

  

  B. 
  

  

  ^C. 
  

  

  D. 
  

  

  In 
  the 
  accompanying 
  table 
  we 
  have 
  endeavored 
  to 
  express 
  

   the 
  affinities 
  and 
  values 
  of 
  the 
  types. 
  In 
  the 
  first 
  column 
  the 
  

   numbers 
  corresponding 
  to 
  the 
  types 
  described. 
  In 
  the 
  second 
  

   column 
  they 
  are 
  grouped 
  under 
  fourteen 
  more 
  comprehensive 
  

   types, 
  which 
  arc 
  indicated 
  by 
  the 
  italic 
  letters. 
  In 
  the 
  third 
  

  

  