﻿352 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Apr. 
  27, 
  

  

  larger 
  than 
  those 
  of 
  the 
  dorsal, 
  ventral, 
  and 
  caudal 
  regions, 
  being 
  

   three 
  times 
  the 
  size 
  of 
  some 
  of 
  the 
  latter 
  ; 
  these 
  scales 
  (lateral 
  tho- 
  

   racic), 
  by 
  their 
  great 
  relative 
  width 
  and 
  greater 
  amount 
  of 
  overlap, 
  

   appear 
  more 
  rectangular 
  in 
  outline 
  than 
  those 
  of 
  other 
  parts 
  of 
  the 
  

   body. 
  The 
  scales 
  of 
  the 
  ventral 
  region 
  are 
  by 
  much 
  the 
  smallest. 
  

   These 
  latter 
  and 
  the 
  scales 
  of 
  the 
  caudal 
  portion 
  of 
  the 
  body 
  are 
  

   those 
  which, 
  by 
  form 
  and 
  ornament, 
  are 
  most 
  typical 
  of 
  the 
  genus 
  

   as 
  established 
  by 
  Agassiz. 
  The 
  scales 
  of 
  the 
  thoracic 
  part 
  of 
  the 
  body 
  

   articulate 
  by 
  means 
  of 
  long, 
  sharply 
  pointed 
  projections 
  from 
  the 
  

   superior 
  margin, 
  which 
  fit 
  into 
  sockets 
  or 
  depressions 
  of 
  the 
  reverse 
  

   and 
  inferior 
  portion 
  of 
  the 
  overlapping 
  scale 
  above, 
  as 
  in 
  Palceoniscus 
  

   and 
  so 
  many 
  other 
  of 
  the 
  Lepidoidei. 
  This 
  system 
  of 
  articulation 
  

   becomes 
  obsolete 
  towards 
  the 
  caudal 
  extremity. 
  The 
  scales 
  of 
  the 
  

   thoracic 
  region, 
  especially 
  the 
  ventral 
  ones, 
  overlap 
  each 
  other 
  more 
  

   than 
  those 
  of 
  the 
  caudal 
  region. 
  All 
  these 
  scales 
  are 
  thick 
  and 
  

   finely 
  enamelled, 
  and 
  are 
  ornamented 
  with 
  two 
  or 
  more 
  converging 
  

   furrows, 
  which 
  always 
  terminate 
  within 
  the 
  margin. 
  Besides, 
  

   however, 
  the 
  scales 
  noticed, 
  there 
  are 
  series 
  of 
  large, 
  oval, 
  pointed, 
  

   bluntly 
  lanceolate, 
  and 
  lanceolate 
  scales, 
  placed 
  in 
  advance 
  of 
  the 
  

   dorsal, 
  anal, 
  and 
  each 
  lobe 
  of 
  the 
  caudal 
  fins. 
  These 
  scales, 
  which 
  

   Agassiz 
  terms 
  the 
  grosses 
  ecailles 
  impaires, 
  attain 
  the 
  length 
  of 
  one- 
  

   third 
  of 
  an 
  inch, 
  and 
  number 
  in 
  each 
  series 
  from 
  four 
  to 
  six 
  ; 
  and 
  

   they 
  would 
  appear 
  to 
  pass 
  by 
  gradations 
  into 
  the 
  long 
  pointed 
  

   fulcral 
  scales 
  or 
  spines 
  that 
  fringe 
  the 
  fins. 
  The 
  surface 
  of 
  these 
  

   scales 
  is 
  closely 
  covered 
  with 
  a 
  similar 
  ornamentation 
  to 
  the 
  other 
  

   scales, 
  but 
  more 
  elaborate 
  than 
  it. 
  

  

  The 
  lateral 
  line 
  is 
  well 
  marked 
  by 
  a 
  series 
  of 
  deeply 
  notched 
  

   and 
  channelled 
  scales 
  in 
  the 
  dorsal 
  half 
  of 
  the 
  body. 
  

  

  None 
  of 
  the 
  specimens 
  discovered 
  show 
  the 
  slightest 
  traces 
  of 
  the 
  

   endoskeleton. 
  

  

  Nevertheless 
  in 
  one 
  example 
  we 
  obtain 
  some 
  idea 
  of 
  the 
  food 
  of 
  this 
  

   Fish 
  ; 
  for, 
  intercalated 
  between 
  the 
  scales 
  of 
  each 
  flank, 
  there 
  may 
  be 
  

   seen 
  portions 
  of 
  a 
  Palceoniscus 
  varians, 
  which 
  undoubtedly 
  represent 
  

   the 
  remains 
  of 
  an 
  undigested 
  individual 
  that 
  had 
  been 
  captured 
  and 
  

   swallowed 
  by 
  the 
  Acrolepis 
  a 
  short 
  time 
  previous 
  to 
  its 
  death. 
  

  

  I 
  at 
  first 
  identified 
  this 
  species 
  with 
  the 
  Acrolepis 
  Sedgtvickii 
  of 
  

   Agassiz 
  ; 
  but 
  later 
  comparisons 
  of 
  my 
  specimens 
  with 
  Agassiz's 
  

   descriptions 
  and 
  figures 
  have 
  shown 
  me 
  that 
  it 
  diners 
  from 
  that 
  

   species 
  in 
  several 
  particulars 
  that 
  appear 
  of 
  importance: 
  for 
  instance, 
  

   the 
  anal 
  fin 
  of 
  A. 
  SedgwicMi 
  is 
  described 
  as 
  being 
  much 
  greater 
  

   than 
  the 
  dorsal, 
  whereas, 
  in 
  the 
  present 
  species, 
  the 
  difference 
  be- 
  

   tween 
  these 
  fins 
  is 
  only 
  slight 
  ; 
  the 
  scales 
  would 
  also 
  appear 
  much 
  

   more 
  regular 
  in 
  size 
  and 
  shape 
  in 
  A. 
  Sedgwickii 
  than 
  in 
  the 
  present 
  

   species; 
  and 
  the 
  former 
  fish 
  would 
  appear 
  to 
  have 
  been 
  twice 
  as 
  

   large 
  as 
  the 
  latter. 
  I 
  therefore 
  cancel 
  the 
  identification 
  I 
  formerly 
  

   made. 
  

  

  From 
  A. 
  asper, 
  Ag\, 
  of 
  the 
  Kupferschiefer, 
  the 
  present 
  species 
  

   differs 
  more 
  than 
  from 
  A. 
  Sedgwichii. 
  But 
  there 
  are 
  four 
  species 
  

   from 
  the 
  same 
  formation, 
  namely, 
  A. 
  angustus, 
  Mimster, 
  A. 
  in- 
  

   termedins, 
  Miinster, 
  A. 
  giganteus, 
  Miinster, 
  and 
  A. 
  exscidptus, 
  

  

  