﻿348 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  differ 
  from 
  the 
  allied 
  species. 
  The 
  plates 
  when 
  present 
  are 
  few 
  and 
  

   small; 
  occasionally 
  one 
  or 
  two 
  may 
  be 
  detected 
  between 
  or 
  beside 
  the 
  

   lobes. 
  

  

  The 
  chitinous 
  processes 
  are 
  very 
  characteristic, 
  though 
  hard 
  to 
  

   describe. 
  The 
  tips 
  of 
  the 
  lobes 
  are 
  quite 
  heavily 
  chitinized, 
  and 
  the 
  proc- 
  

   esses 
  extending 
  cephalad 
  along 
  the 
  inner 
  margins 
  of 
  the 
  median 
  lobes 
  

   are 
  usually 
  comparatively 
  large 
  and 
  distinct. 
  Newell, 
  in 
  his 
  Iowa 
  bul- 
  

   letin 
  no. 
  43, 
  p. 
  i6i, 
  speaks 
  of 
  these 
  as 
  sharp 
  pointed 
  and 
  curved 
  in 
  con- 
  

   tradistinction 
  to 
  the 
  almost 
  straight 
  ones 
  of 
  A. 
  ancylus. 
  This 
  

   difference, 
  if 
  constant, 
  takes 
  very 
  careful 
  focusing 
  to 
  determine, 
  and 
  is 
  

   not 
  striking, 
  as 
  is 
  proven 
  by 
  the 
  fact 
  that 
  other 
  illustrators 
  of 
  the 
  species 
  

   have 
  not 
  brought 
  it 
  out. 
  Indeed, 
  the 
  original 
  figure 
  represents 
  these 
  

   processes 
  as 
  straight 
  and 
  quite 
  different 
  in 
  shape 
  from 
  NewelPs 
  figure. 
  

   This 
  point 
  is 
  probably 
  good 
  additional 
  evidence 
  of 
  the 
  identity 
  of 
  the 
  

   species 
  when 
  it 
  can 
  be 
  definitely 
  ascertained, 
  but 
  is 
  not 
  the 
  most 
  

   obvious 
  and 
  easiest 
  criterion. 
  There 
  is 
  also 
  an 
  extension 
  of 
  chitin 
  

   cephalad 
  near 
  the 
  outer 
  margin 
  of 
  the 
  median 
  lobes. 
  

  

  The 
  chitinous 
  processes 
  on 
  the 
  inner 
  margin 
  of 
  the 
  first 
  incision 
  are 
  

   large, 
  much 
  larger 
  than 
  those 
  opposite. 
  They 
  are 
  almost 
  pear-shaped 
  

   with 
  a 
  compound 
  curve 
  on 
  the 
  side 
  toward 
  the 
  median 
  line. 
  That 
  is, 
  

   they 
  are 
  often 
  abruptly 
  narrowed 
  toward 
  the 
  tip 
  and 
  outer 
  margin 
  of 
  the 
  

   lobe 
  with 
  a 
  full 
  curve 
  to 
  the 
  very 
  broad 
  and 
  plump 
  cephalic 
  part. 
  This 
  

   may 
  seem 
  a 
  hazy 
  description 
  till 
  somewhat 
  cleared 
  by 
  study 
  of 
  the 
  

   figures 
  and 
  by 
  familiarity 
  with 
  the 
  forms. 
  As 
  a 
  matter 
  of 
  fact 
  these 
  

   chitinous 
  processes 
  are 
  quite 
  distinctive 
  in 
  A. 
  f 
  o 
  r 
  b 
  e 
  s 
  i 
  being 
  easily 
  dis- 
  

   tinguished 
  from 
  the 
  more 
  indefinite 
  and 
  irregular 
  ones 
  of 
  A. 
  ostreae- 
  

   f 
  o 
  r 
  m 
  i 
  s 
  and 
  A. 
  ancylus 
  and 
  somewhat 
  less 
  certainly 
  from 
  A. 
  p 
  e 
  r 
  - 
  

   n 
  i 
  c 
  i 
  o 
  s 
  us 
  by 
  the 
  narrower 
  distal 
  part, 
  and 
  specially 
  by 
  the 
  usually 
  marked 
  

   superiority 
  in 
  size 
  to 
  the 
  opposite 
  process, 
  while 
  in 
  A. 
  perniciosus 
  

   the 
  two 
  processes 
  are 
  subequal. 
  The 
  chitinous 
  processes 
  about 
  the 
  

   small 
  second 
  incision 
  vary 
  more 
  than 
  in 
  the 
  case 
  of 
  the 
  first 
  incision. 
  

  

  The 
  adult 
  female 
  shows 
  ventral 
  glands 
  in 
  5 
  groups. 
  Johnson 
  gives 
  

   1-3 
  for 
  the 
  anterior 
  group, 
  3-7 
  for 
  the 
  anterior 
  laterals 
  and 
  3-5 
  for 
  the 
  

   posterior 
  laterals. 
  The 
  general 
  arrangement 
  of 
  these 
  is 
  somewhat 
  linear. 
  

  

  The 
  ventral 
  chitinous 
  thickenings 
  within 
  the 
  posterior 
  lateral 
  groups 
  

   are 
  nearly 
  straight 
  and 
  club-shaped 
  and 
  are 
  usually 
  narrow 
  and 
  definite, 
  

   as 
  stated 
  above. 
  Sometimes 
  a 
  fainter, 
  less 
  heavily 
  chitinized 
  fold 
  or 
  fork 
  

   appears, 
  but 
  the 
  main 
  and 
  obvious 
  process 
  is 
  more 
  or 
  less 
  nearly 
  as 
  illus- 
  

   trated 
  and 
  is 
  usually 
  in 
  line 
  with 
  a 
  small, 
  straight, 
  more 
  heavily 
  chitinized 
  

   portion 
  of 
  the 
  general 
  thickening 
  inward 
  from 
  the 
  base 
  of 
  the 
  lobes 
  men- 
  

   tioned 
  in 
  the 
  paragraph 
  for 
  the 
  explanation 
  of 
  terms. 
  

  

  