﻿CLASSIFICATION, 
  ETC. 
  OP 
  HAMILTON 
  AND 
  CHEMUNG 
  SERIES 
  325 
  

  

  Fig. 
  5. 
  Bothriolepis 
  minor 
  Newb. 
  An- 
  

   tedorso-median 
  plate 
  denuded 
  of 
  

   outer 
  crust. 
  

  

  and 
  with 
  the 
  exception 
  of 
  fig. 
  7, 
  all 
  turned 
  with 
  the 
  posterior 
  

   end 
  uppermost. 
  

  

  The 
  orientation 
  of 
  this 
  plate 
  is 
  capable 
  of 
  positive 
  determina- 
  

   tion, 
  whether 
  the 
  rugose 
  external 
  crust 
  is 
  preserved, 
  or 
  only 
  an 
  im- 
  

   pression 
  of 
  the 
  visceral 
  surface 
  of 
  the 
  

   bone 
  remains. 
  In 
  case 
  the 
  ornamenta- 
  

   tion 
  is 
  preserved 
  well 
  enough 
  to 
  show 
  

   the 
  divergent 
  sensory 
  canals, 
  it 
  need 
  

   only 
  be 
  borne 
  in 
  mind 
  that 
  these 
  meet 
  

   at 
  an 
  angle 
  near 
  the 
  center 
  of 
  the 
  plate 
  

   with 
  the 
  apex 
  of 
  the 
  V 
  directed 
  an- 
  

   teriorly. 
  When 
  the 
  bone-substance 
  has 
  

   been 
  denuded 
  so 
  as 
  to 
  leave 
  a 
  smooth 
  

   impression 
  of 
  the 
  visceral* 
  surface, 
  as 
  

   shown 
  in 
  fig. 
  4, 
  we 
  notice 
  first 
  of 
  all 
  a 
  

   median 
  keel, 
  which 
  traverses 
  the 
  plate 
  

   for 
  about 
  three 
  quarters 
  of 
  its 
  length. 
  Frequently 
  the 
  keel 
  

   itself 
  is 
  more 
  or 
  less 
  worn 
  away, 
  its 
  position 
  being 
  marked 
  by 
  a 
  

   longitudinal 
  groove, 
  widest 
  a 
  little 
  in 
  advance 
  of 
  the 
  middle 
  of 
  

   the 
  plate, 
  and 
  terminating 
  slightly 
  before 
  the 
  posterior 
  margin. 
  

   The 
  keel 
  is 
  met 
  on 
  either 
  side 
  anteriorly 
  (at 
  a 
  distance 
  behind 
  the 
  

   anterior 
  margin 
  equal 
  to 
  about 
  one 
  fourth 
  the 
  length 
  of 
  the 
  plate) 
  

   by 
  a 
  sharp 
  ridge 
  depending 
  from 
  the 
  under 
  surface, 
  and 
  extend- 
  

   ing 
  forward 
  and 
  outward 
  nearly 
  to 
  the 
  anterior 
  margin. 
  These 
  

   ridges 
  diverge 
  from 
  the 
  median 
  keel 
  at 
  a 
  somewhat 
  lesser 
  angle 
  

   than 
  that 
  formed 
  by 
  the 
  junction 
  of 
  the 
  sensory 
  canals, 
  and 
  it 
  

   often 
  happens 
  that 
  the 
  area 
  included 
  between 
  them 
  is 
  broken 
  

   off 
  from 
  the 
  rest 
  of 
  the 
  plate. 
  In 
  some 
  specimens 
  the 
  keel 
  ap- 
  

   pears 
  to 
  terminate 
  at 
  the 
  junction 
  of 
  these 
  ridges, 
  but 
  in 
  others 
  

   it 
  continues 
  faintly 
  almost 
  as 
  far 
  as 
  the 
  anterior 
  margin. 
  

  

  Apparently 
  some 
  structural 
  difference 
  exists 
  between 
  the 
  bor- 
  

   ders 
  of 
  the 
  plate 
  where 
  it 
  overlaps 
  contiguous 
  elements 
  (ante- 
  

   dorso-laterals), 
  and 
  the 
  central 
  portion. 
  Possibly 
  the 
  bone 
  is 
  

   denser 
  near 
  the 
  edges 
  than 
  elsewhere, 
  but 
  at 
  all 
  events 
  it 
  is 
  usual 
  

   to 
  find 
  the 
  margins 
  preserved 
  as 
  far 
  as 
  they 
  are 
  overlapped, 
  even 
  

   where 
  the 
  ornament 
  has 
  been 
  worn 
  smooth 
  as 
  shown 
  in 
  the 
  

  

  