﻿1864.] 
  LANKESTEK 
  SCALES 
  OF 
  PTEEASPIS. 
  197 
  

  

  are 
  marked 
  by 
  similar 
  minute 
  lines 
  running 
  parallel 
  with 
  the 
  sides 
  

   of 
  the 
  scute 
  to 
  which 
  they 
  are 
  attached. 
  The 
  piece 
  between 
  the 
  

   rostrum 
  and 
  dorsal 
  scute 
  in 
  which 
  the 
  orbits 
  are 
  placed 
  is 
  orna- 
  

   mented 
  by 
  a 
  series 
  of 
  curved 
  striations, 
  parallel 
  with 
  the 
  margins 
  

   of 
  the 
  orbital 
  apertures 
  (e, 
  and 
  fig. 
  2). 
  The 
  striations 
  on 
  the 
  ros- 
  

   trum 
  run 
  in 
  parallels 
  across 
  the 
  median 
  line, 
  describing 
  four 
  curves, 
  

   which 
  become 
  one 
  at 
  the 
  termination 
  of 
  the 
  snout 
  (fig. 
  10 
  d). 
  Be- 
  

   tween 
  the 
  rostrum 
  and 
  the 
  scute 
  a 
  small 
  quadrangular 
  piece 
  exists, 
  

   in 
  which 
  the 
  markings 
  are 
  arranged 
  somewhat 
  differently 
  (see 
  

   figure). 
  Besides 
  these 
  delicate 
  striae, 
  there 
  are 
  found 
  on 
  the 
  dorsal 
  

   scute 
  two 
  series 
  of 
  minute 
  round 
  depressions, 
  one 
  on 
  each 
  side. 
  

   Another 
  series 
  surrounds 
  the 
  insertion 
  of 
  the 
  spine, 
  and 
  a 
  third 
  

   and 
  fourth 
  run 
  from 
  the 
  posterior 
  angles 
  towards 
  the 
  central 
  ele- 
  

   vation. 
  The 
  posterior 
  spine 
  itself 
  is 
  devoid 
  of 
  any 
  markings 
  ; 
  a 
  

   large 
  portion 
  of 
  it 
  is 
  filled 
  into 
  the 
  back 
  of 
  the 
  scute 
  as 
  a 
  distinct 
  

   piece. 
  

  

  The 
  internal 
  aspect 
  of 
  the 
  shield 
  presents 
  a 
  surface 
  quite 
  

   free 
  from 
  any 
  ornamentations 
  in 
  the 
  form 
  of 
  striae, 
  being 
  composed 
  

   of 
  the 
  nacreous 
  or 
  internal 
  layer 
  of 
  Prof. 
  Huxley. 
  The 
  most 
  

   prominent 
  feature 
  is 
  a 
  small 
  circular 
  depression 
  which 
  corre- 
  

   sponds 
  to 
  the 
  quadrangular 
  piece 
  mentioned 
  as 
  existing 
  on 
  the 
  

   convex 
  side. 
  Two 
  very 
  conspicuous 
  elevations 
  exist 
  also 
  on 
  either 
  

   side 
  of 
  the 
  median 
  line, 
  immediately 
  beneath 
  the 
  elevated 
  boss 
  of 
  the 
  

   outer 
  surface. 
  Certain 
  inequalities 
  of 
  surface 
  also 
  exist, 
  which 
  cor- 
  

   respond 
  to 
  the 
  contour 
  of 
  the 
  exterior. 
  The 
  sutures 
  visible 
  on 
  the 
  

   exterior, 
  where 
  the 
  various 
  portions 
  of 
  which 
  the 
  plate 
  is 
  composed 
  

   are 
  joined, 
  are 
  not 
  obvious 
  on 
  the 
  concave 
  surface. 
  

  

  These 
  few 
  remarks 
  are 
  merely 
  intended 
  as 
  a 
  small 
  contribution 
  

   to 
  our 
  knowledge 
  of 
  this 
  most 
  interesting 
  Fish. 
  Further 
  researches 
  

   and 
  discoveries 
  are 
  still 
  needed 
  to 
  elucidate 
  the 
  form 
  of 
  the 
  fins 
  and 
  

   of 
  a 
  large 
  portion 
  of 
  the 
  body 
  ; 
  and 
  it 
  is 
  to 
  be 
  hoped 
  that 
  it 
  will 
  

   not 
  be 
  long 
  ere 
  tolerably 
  perfect 
  specimens 
  of 
  this 
  genus 
  will 
  be 
  

   exhumed 
  from 
  the 
  Cornstones 
  of 
  Herefordshire. 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XII. 
  

  

  Illustrative 
  of 
  the 
  Scales 
  and 
  Cephalic 
  Shield 
  of 
  Pteraspis. 
  

  

  Fig. 
  1. 
  Diagram 
  of 
  the 
  Scales 
  of 
  Pteraspis. 
  

  

  2. 
  Diagram 
  of 
  a 
  portion 
  of 
  the 
  cephalic 
  shield 
  of 
  Pteraspis, 
  showing 
  

  

  striations 
  parallel 
  to 
  the 
  margin 
  of 
  the 
  orbital 
  aperture. 
  

   Figs. 
  3 
  & 
  4. 
  Portion 
  of 
  the 
  cephalic 
  shield 
  of 
  Pteraspis, 
  with 
  scales 
  attached 
  to 
  

  

  the 
  posterior 
  margin. 
  Natural 
  size. 
  

   Fig. 
  5. 
  Diagram-sections 
  of 
  the 
  cephalic 
  shield 
  of 
  Pteraspis 
  : 
  a, 
  from 
  rostrum 
  

  

  to 
  spine 
  ; 
  b, 
  from 
  side 
  to 
  side. 
  

   Figs. 
  6 
  & 
  7. 
  Diagrams 
  illustrating 
  the 
  arrangement 
  of 
  the 
  scales 
  of 
  Pteraspis. 
  

  

  8 
  & 
  9. 
  Diagram 
  of 
  the 
  Scales 
  of 
  Cephalaspis. 
  

   Fig. 
  10. 
  Eestoration 
  of 
  the 
  cephalic 
  shield 
  of 
  Pteraspis 
  : 
  a, 
  margin 
  ; 
  b, 
  lateral 
  

  

  cornua 
  ; 
  c, 
  orbital 
  region 
  ; 
  d, 
  rostrum 
  ; 
  e, 
  dorsal 
  spine. 
  

  

  