﻿48 
  Descriptions 
  of 
  New 
  Species 
  and 
  Varieties 
  of 
  Shells, 
  

  

  Probably 
  the 
  specimens 
  before 
  me 
  are 
  immature, 
  but 
  the 
  

   species 
  is 
  quite 
  distinct 
  from 
  any 
  other. 
  

  

  Of 
  Planorbis 
  dentiferus 
  Ad., 
  (Proc. 
  Bost. 
  Soc. 
  Jan. 
  1, 
  

   1845,) 
  a 
  variety 
  occurs, 
  which 
  is 
  destitute 
  of 
  teeth 
  ! 
  After 
  a 
  

   careful 
  examination 
  of 
  many 
  specimens, 
  I 
  am 
  unable 
  to 
  find 
  

   any 
  other 
  differences 
  constantly 
  associated 
  with 
  this 
  peculiar- 
  

   ity. 
  Many 
  of 
  the 
  toothless 
  shells 
  are 
  more 
  compressed 
  oblique- 
  

   ly 
  just 
  below 
  the 
  periphery, 
  than 
  the 
  type, 
  but 
  the 
  same 
  is 
  

   true 
  of 
  some 
  of 
  the 
  shells 
  in 
  which 
  the 
  teeth 
  are 
  well 
  devel- 
  

   oped. 
  It 
  is 
  not 
  a 
  local 
  variety, 
  both 
  kinds 
  occurring 
  together 
  

   at 
  Hatfield, 
  in 
  Westmoreland. 
  The 
  variety 
  may 
  be 
  designa- 
  

   ted 
  by 
  the 
  name 
  edentatus. 
  

  

  Ancylus 
  obliquus. 
  Shell 
  subovate, 
  somewhat 
  arcuate, 
  

   very 
  convex 
  : 
  translucent, 
  pale 
  horn 
  color 
  : 
  extremely 
  thin, 
  

   with 
  microscopic 
  radiating 
  raised 
  lines, 
  and 
  less 
  distinct 
  striae 
  

   of 
  growth 
  : 
  apex 
  very 
  prominent, 
  elevated, 
  extending 
  very 
  far 
  

   to 
  one 
  side 
  and 
  posteriorly, 
  and 
  projecting 
  nearly 
  over 
  the 
  

   margin. 
  

  

  Length 
  .075 
  inch 
  ; 
  breadth 
  .05 
  inch 
  ; 
  height 
  .028 
  inch. 
  

  

  This 
  remarkable 
  shell 
  may 
  belong 
  to 
  a 
  new 
  genus, 
  but 
  

   without 
  the 
  soft 
  parts, 
  it 
  is 
  difficult 
  to 
  determine 
  the 
  generic 
  

   value 
  of 
  its 
  peculiarities. 
  The 
  shell 
  is 
  hitherto 
  unique 
  in 
  the 
  

   rich 
  collection 
  of 
  the 
  Hon. 
  Edward 
  Chitty, 
  to 
  whom 
  I 
  am 
  in- 
  

   debted 
  for 
  the 
  loan 
  of 
  it. 
  

  

  Truncatella 
  modesta. 
  Shell 
  much 
  elongate, 
  ovate 
  conic 
  : 
  

   yellowish 
  horn 
  color, 
  with 
  a 
  white 
  upper 
  margin 
  of 
  the 
  whorls 
  : 
  

   with 
  about 
  twenty-one 
  prominent 
  compressed 
  ribs, 
  and 
  nu- 
  

   merous 
  spiral 
  striae, 
  which 
  are 
  interrupted 
  by 
  the 
  ribs 
  : 
  apex 
  

  

  truncate 
  with 
  the 
  loss 
  of 
  whorls 
  : 
  spire 
  with 
  the 
  outlines 
  

  

  somewhat 
  curvilinear 
  : 
  whorls 
  remaining 
  after 
  truncation 
  

   seven, 
  moderately 
  convex, 
  margined 
  above 
  : 
  aperture 
  subovate, 
  

   slightly 
  angulated 
  anteriorly. 
  

  

  