﻿2IO 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  terior 
  basal 
  margin, 
  and 
  above 
  this 
  the 
  surface 
  of 
  the 
  posterior 
  wing 
  

   is 
  sHghtly 
  concave; 
  beaks 
  incurved, 
  hardly 
  raised 
  above 
  the 
  hinge 
  

   line; 
  posterior 
  end 
  more 
  sharply 
  rounded 
  than 
  anterior; 
  surface 
  with 
  

   concentric 
  striae. 
  

  

  Found 
  in 
  the 
  Clinton 
  lenses 
  on 
  the 
  Rome, 
  Watertown 
  and 
  Og- 
  

   densburg 
  railroad. 
  

  

  Class 
  GASTROPODA 
  Cuvier 
  

  

  The 
  gastropods, 
  or 
  snails, 
  are 
  mollusks 
  with 
  a 
  distinct 
  head, 
  a 
  

   muscular 
  foot, 
  and 
  a 
  mantle 
  consisting 
  of 
  a 
  single 
  lobe. 
  They 
  are 
  

   terrestrial, 
  marine, 
  or 
  fresh-water 
  animals, 
  ^nd 
  are 
  commonly 
  pro- 
  

   tected 
  by 
  a 
  conic 
  or 
  spirally 
  coiled 
  shell, 
  which 
  is 
  secreted 
  by 
  the 
  

   mantle. 
  The 
  apical 
  part 
  of 
  the 
  shell 
  usually 
  consists 
  of 
  a 
  simple 
  

   coiled 
  embryonic 
  shell, 
  or 
  protoconch. 
  Succeeding 
  this 
  is 
  the 
  shell 
  

   proper, 
  which, 
  when 
  coiled 
  comprises 
  few 
  or 
  many 
  whorls, 
  the 
  later 
  

   overlapping 
  the 
  earlier 
  ones 
  to 
  a 
  greater 
  or 
  less 
  extent. 
  The 
  suture 
  

   at 
  the 
  junction 
  of 
  the 
  overlapping 
  whorls 
  may 
  be 
  faintly 
  or 
  strongly 
  

   impressed. 
  The 
  whorls 
  may 
  coil 
  closely, 
  forming 
  a 
  compact 
  central 
  

   columella; 
  or 
  they 
  may 
  be 
  loosely 
  *coiled, 
  leaving 
  a 
  hollow 
  columella, 
  

   opening 
  below 
  in 
  the 
  umbilicus. 
  The 
  body 
  whorl 
  opens 
  in 
  the 
  

   aperture, 
  the 
  rim 
  or 
  peristome 
  of 
  which 
  consists 
  of 
  an 
  outer 
  and 
  an 
  

   inner, 
  or 
  columellar 
  lip. 
  The 
  peristome 
  is 
  complete 
  when 
  both 
  inner 
  

   and 
  outer 
  lip 
  are 
  present, 
  and 
  incomplete 
  when 
  the 
  place 
  of 
  the 
  inner 
  

   lip 
  is 
  taken 
  by 
  the 
  preceding 
  whorl. 
  In 
  a 
  great 
  many 
  species 
  the 
  

   peristome 
  is 
  notched 
  anteriorly, 
  or 
  produced 
  into 
  a 
  straight, 
  or 
  more 
  

   or 
  less 
  flexed 
  canal. 
  A 
  posterior 
  notch 
  is 
  also 
  frequently 
  found. 
  

   The 
  columellar 
  lip 
  and, 
  in 
  its 
  absence, 
  the 
  columella, 
  njay 
  be 
  smooth 
  

   or 
  furnished 
  with 
  one 
  or 
  more 
  plications. 
  Similarly, 
  the 
  outer 
  lip 
  

   may 
  be 
  smooth 
  on 
  its 
  inner 
  side 
  or 
  furnished 
  with 
  plications 
  or 
  

   Hrae. 
  Among 
  the 
  external 
  features 
  of 
  importance 
  are 
  the 
  transverse 
  

   lines 
  of 
  growth, 
  which 
  mark 
  the 
  successive 
  increments; 
  varices 
  or 
  

   rows 
  of 
  spines, 
  parallel 
  to 
  the 
  lines 
  of 
  growth, 
  and 
  marking 
  periodic 
  

   resting 
  stages 
  during 
  the 
  growth 
  of 
  the 
  shell; 
  and 
  revolving 
  longi- 
  

   tudinal 
  lines 
  or 
  ridges, 
  which 
  may 
  be 
  uniform 
  or 
  alternating, 
  or 
  may 
  

   show 
  a 
  gradation 
  in 
  size. 
  When 
  transverse 
  and 
  longitudinal 
  lines 
  

   cross 
  each 
  other, 
  a 
  reticulated 
  surface 
  ornamentation 
  is 
  produced; 
  

   and, 
  when 
  the 
  shell 
  is 
  covered 
  by 
  an 
  epidermis, 
  or 
  periostracum, 
  hair- 
  

   like 
  spines 
  not 
  infrequently 
  arise 
  from 
  the 
  points 
  of 
  crossing. 
  In 
  

   Pleurotomaria 
  and 
  related 
  gastropods, 
  a 
  siphonal 
  notch 
  occurs 
  in 
  

   the 
  outer 
  lip, 
  and 
  its 
  progressive 
  closure 
  from 
  behind 
  leaves 
  a 
  

   marked 
  revolving 
  band, 
  commonly 
  visible 
  only 
  on 
  the 
  body 
  whorl. 
  

  

  Many 
  species, 
  specially 
  of 
  marine 
  gastropods, 
  secrete 
  a 
  horny 
  or, 
  

   calcareous 
  operculum, 
  which 
  is 
  attached 
  to 
  the 
  foot, 
  and 
  closes 
  the 
  

   aperture 
  of 
  the 
  shell 
  when 
  the 
  animal 
  is 
  withdrawn. 
  This 
  is 
  seldomi 
  

   preserved 
  in 
  a 
  fossil 
  state. 
  

  

  