﻿206 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  3 
  

  

  rotund; 
  cardinal 
  slopes 
  meeting 
  in 
  obtuse 
  angle; 
  young 
  shell 
  car- 
  

   inate 
  toward 
  the 
  beak 
  in 
  the 
  pedicle 
  valve; 
  

   brachial 
  valve 
  gently 
  convex; 
  median 
  fold 
  

   beginning 
  as 
  a 
  depression 
  at 
  the 
  beak, 
  and 
  

   becoming 
  elevated 
  near 
  the 
  front; 
  two 
  plica- 
  

   tions 
  in 
  sinus, 
  three 
  on 
  fold; 
  sharp 
  rounded 
  

   plications; 
  strong 
  frontal 
  sinuosity; 
  very 
  fine 
  

   concentric 
  striae. 
  

   Found 
  in 
  great 
  abundance 
  in 
  the 
  lower 
  Clinton 
  limestone 
  at 
  

  

  Niagara. 
  Also 
  east 
  of 
  Lockport 
  (Hall). 
  

  

  Fig. 
  133 
  Anoplothica 
  plicatula 
  

  

  Class 
  PELECYPODA 
  Goldfuss 
  

   (Lamellibranchiata 
  Blainville) 
  

  

  The 
  Pelecypoda, 
  or 
  Lamellibranchiata, 
  are 
  marine 
  or 
  fresh-water 
  

   mollusks, 
  with 
  a 
  bivalve 
  shell. 
  The 
  valves 
  are 
  complementary, 
  and 
  

   in 
  the 
  majority 
  of 
  species 
  are 
  of 
  nearly 
  similar 
  outline 
  and 
  size. 
  In 
  

   each 
  valve 
  may 
  be 
  distinguished 
  

   an 
  initial 
  point, 
  or 
  beak, 
  around 
  

   which 
  the 
  concentric 
  lines 
  of 
  

   growth 
  mark 
  the 
  successive 
  ad- 
  

   ditions 
  of 
  shelly 
  matter. 
  

  

  The 
  orientation 
  of 
  most 
  shells 
  

   is 
  effected 
  by 
  holding 
  them 
  with 
  

   the 
  hinge 
  line 
  uppermost 
  and 
  the 
  

   beaks 
  pointing 
  away 
  from 
  the 
  

   observer. 
  Thus 
  placed, 
  the 
  up- 
  

   per 
  is 
  the 
  dorsal 
  and 
  the 
  lower 
  

   the 
  ventral 
  border. 
  The 
  end 
  far- 
  

   thest 
  away 
  from 
  the 
  

   is 
  the 
  anterior 
  end; 
  that 
  nearest, 
  the 
  posterior 
  end. 
  The 
  valves 
  are 
  

   designated 
  as 
  the 
  right 
  and 
  left 
  valves 
  respectively. 
  The 
  articula- 
  

   tion 
  of 
  the 
  valves 
  is 
  commonly 
  effected 
  by 
  the 
  interlocking 
  of 
  

   teeth 
  which 
  are 
  borne 
  on 
  the 
  hinge 
  or 
  cardinal 
  margin 
  of 
  the 
  valves. 
  

   They 
  vary 
  greatly, 
  but 
  can 
  usually 
  be 
  divided 
  into 
  the 
  short, 
  stout 
  

   cardinal 
  teeth, 
  which 
  are 
  situated 
  under 
  or 
  near 
  the 
  beak, 
  and 
  the 
  

   ridge-like 
  lateral 
  teeth. 
  The 
  opening 
  of 
  the 
  valves 
  is 
  brought 
  about 
  

   by 
  an 
  elastic 
  ligament 
  stretched 
  across 
  the 
  hinge 
  from 
  valve 
  to 
  

   valve, 
  behind 
  the 
  beak, 
  which 
  acts, 
  on 
  the 
  principle 
  of 
  the 
  C 
  spring, 
  

   whenever 
  the 
  tension 
  of 
  the 
  adductor 
  muscles, 
  which 
  close 
  the 
  valves, 
  

   is 
  relaxed. 
  In 
  many 
  genera, 
  an 
  elastic, 
  compressible 
  cartilage, 
  the 
  

  

  Fig. 
  134 
  Diagrammatic 
  view 
  of 
  left 
  valve 
  of 
  

   Cytherea; 
  (aa) 
  anterior 
  adductor 
  scars; 
  (pa) 
  

   posterior 
  adductor 
  scars; 
  (pl) 
  pallial 
  line; 
  (ps) 
  

   observer 
  l^^'^^^ 
  sinus; 
  (t) 
  teeth; 
  (um) 
  umbo; 
  (1) 
  ligament 
  

  

  