﻿VEKTEBBATES. 
  199 
  

  

  from 
  a 
  locality 
  consists 
  not 
  of 
  a 
  single 
  form 
  merely, 
  but 
  of 
  indi- 
  

   viduals 
  pertaining 
  to 
  the 
  same 
  side 
  in 
  relation 
  to 
  their 
  position 
  upon 
  

   the 
  jaws. 
  However, 
  fortunately, 
  now 
  and 
  then 
  appears 
  a 
  specimen 
  

   which 
  seems 
  to 
  set 
  at 
  rest 
  whatever 
  doubts 
  may 
  have 
  been 
  enter- 
  

   tained 
  as 
  to 
  the 
  actual 
  state 
  of 
  things, 
  and 
  in 
  a 
  few 
  of 
  the 
  species 
  

   the 
  collections 
  are 
  rich 
  in 
  data 
  going 
  to 
  establish 
  a 
  more 
  precise 
  

   and 
  comprehensive 
  understanding 
  of 
  the 
  species 
  themselves 
  and 
  the 
  

   family 
  and 
  ordinal 
  relations 
  of 
  the 
  genus. 
  

  

  So 
  far 
  as 
  has 
  come 
  to 
  the 
  notice 
  of 
  the 
  writers, 
  the 
  genus 
  Psam- 
  

   moclus 
  has 
  been 
  classed 
  by 
  authors 
  with 
  the 
  Cestracionts 
  ; 
  Dr. 
  L. 
  de 
  

   Koninck, 
  however, 
  recognizing 
  their 
  distinct 
  family 
  character, 
  for 
  

   which 
  he 
  proposed 
  the 
  term 
  Psammodonticlas.* 
  As 
  early 
  as 
  1843, 
  

   Captain 
  Jones, 
  in 
  a 
  communication 
  in 
  reference 
  to 
  his 
  acquisitions 
  

   of 
  fish 
  remains 
  from 
  the 
  mountain 
  limestone 
  localities 
  in 
  the 
  vicinity 
  

   of 
  Armagh, 
  says 
  : 
  "There 
  are 
  good 
  specimens 
  of 
  one 
  more 
  tooth, 
  

   somewhat 
  allied 
  to 
  Psammodus, 
  yet 
  having 
  a 
  distinct 
  character, 
  which 
  

   will 
  connect 
  it 
  with 
  the 
  Myliobates 
  ;"t 
  and 
  to 
  whom 
  should 
  be 
  cred- 
  

   ited 
  thus 
  early 
  the 
  recognition 
  of 
  the 
  affinities 
  of 
  the 
  Psammodonts. 
  

  

  The 
  examination 
  of 
  a 
  considerable 
  suite 
  of 
  the 
  teeth 
  of 
  Psammo- 
  

   dus 
  must 
  convince 
  one 
  of 
  their 
  having 
  originally 
  occupied 
  a 
  serial 
  

   position 
  upon 
  the 
  jaws, 
  stretching 
  across 
  from 
  side 
  to 
  side, 
  in 
  the 
  

   manner 
  exemplified 
  by 
  the 
  Myliobates 
  of 
  Tertiary 
  and 
  existing 
  seas. 
  

   Indeed, 
  Dr. 
  de 
  Koninck 
  alludes, 
  loc. 
  c, 
  to 
  a 
  series 
  of 
  three 
  teeth 
  of 
  

   the 
  species 
  P. 
  porosus, 
  found 
  by 
  Mr. 
  Neilson 
  in 
  the 
  mountain 
  lime- 
  

   stone 
  deposits 
  near 
  Glasgow 
  (N. 
  B.), 
  which 
  still 
  retain 
  their 
  relative 
  

   position 
  to 
  one 
  another, 
  and 
  with 
  which 
  the 
  distinguished 
  palaeon- 
  

   tologist 
  reconstructs 
  the 
  dental 
  armament 
  of 
  the 
  jaw. 
  But 
  perhaps 
  

   the 
  most 
  complete 
  and 
  satisfactory 
  information 
  to 
  be 
  derived 
  from 
  

   isolated 
  detached 
  teeth 
  is 
  that 
  secured 
  by 
  Mr. 
  Springer 
  of 
  the 
  species 
  

   bearing 
  his 
  name, 
  from 
  the 
  Upper 
  Burlington 
  limestone 
  of 
  our 
  Lower 
  

   Carboniferous 
  series. 
  The 
  latter 
  are 
  so 
  well 
  preserved 
  as 
  to 
  furnish 
  

   many 
  and 
  highly 
  desirable 
  details 
  without 
  which 
  still 
  some 
  uncer- 
  

   tainty 
  might 
  intervene 
  to 
  a 
  satisfactory 
  conclusion 
  on 
  the 
  chief 
  points 
  

   relating 
  to 
  the 
  disposition 
  of 
  the 
  teeth 
  upon 
  the 
  jaws. 
  These 
  show 
  

   conclusively 
  that 
  the 
  teeth 
  were 
  arranged 
  in 
  at 
  least 
  double 
  rows, 
  

   not 
  exactly 
  opposite, 
  but 
  the 
  tooth 
  of 
  one 
  or 
  other 
  row 
  in 
  advance 
  

   of 
  its 
  mate, 
  the 
  articular 
  border 
  showing 
  obliquely 
  truncated 
  facets 
  

   at 
  one 
  or 
  other 
  angle 
  by 
  which 
  it 
  is 
  coadapted 
  to 
  the 
  articular 
  faces 
  

  

  *Faune 
  du 
  Calcaire 
  Carbonifere 
  de 
  la 
  Belgirjue, 
  11, 
  p. 
  38, 
  1878. 
  

  

  tUeport 
  on 
  the 
  Geology 
  of 
  Londonderry, 
  etc. 
  by 
  J. 
  E. 
  Portlock, 
  F. 
  U.S., 
  F. 
  G. 
  S., 
  etc., 
  

   1843, 
  p. 
  462. 
  

  

  