﻿OF 
  THE 
  MORAY 
  FIRTH 
  AREA. 
  

  

  261 
  

  

  Association 
  at 
  Oxford 
  in 
  1894, 
  under 
  the 
  name 
  of 
  MegalaspU 
  

   Taijlori. 
  Proceeding 
  immediately 
  thereafter 
  to 
  the 
  British 
  Museum, 
  

   on 
  inquiring 
  for 
  Psammosteus, 
  Mr. 
  Smith 
  "Woodward 
  showed 
  me, 
  

   among 
  other 
  specimens, 
  two 
  papier-mache 
  casts 
  of 
  tolerably 
  entire 
  

   plates 
  of 
  P. 
  paradoxus, 
  Ag., 
  from 
  Russia, 
  by 
  which 
  my 
  doubts 
  were 
  

   at 
  once 
  solved, 
  and 
  in 
  the 
  ' 
  Annals 
  of 
  Scottish 
  Natal] 
  History 
  ' 
  for 
  

   October 
  of 
  that 
  year 
  I 
  published, 
  under 
  the 
  name 
  of 
  Psammosteus 
  

   Taylori, 
  an 
  outline 
  sketch 
  of 
  a 
  specimen 
  presented 
  by 
  Mr. 
  Taylor 
  

   to 
  the 
  Edinburgh 
  Museum. 
  Subsequently 
  collected 
  material 
  

   has 
  completely 
  confirmed 
  this 
  determination 
  ; 
  among 
  other 
  things, 
  

   the 
  external 
  ornament 
  has 
  now 
  been 
  discovered 
  in 
  Newton 
  speci- 
  

   mens, 
  thereby 
  proving 
  the 
  identity 
  with 
  them 
  of 
  Mr. 
  Miller's 
  

   fragment 
  from 
  Balnagown. 
  

  

  Description. 
  — 
  Large 
  oblong 
  plates, 
  gently 
  hollowed 
  in 
  boat-like 
  

   fashion, 
  but 
  more 
  concave 
  from 
  side 
  to 
  side 
  than 
  from 
  back 
  to 
  

   front, 
  and 
  more 
  concave 
  posteriorly 
  than 
  anteriorly 
  ; 
  truncated 
  

   and 
  obtusely 
  indented 
  in 
  front 
  j 
  sides 
  slightly 
  concave 
  anteriorly, 
  

   then 
  becoming 
  convex, 
  so 
  that 
  the 
  greatest 
  width 
  of 
  the 
  plate 
  is 
  

   behind 
  its 
  middle 
  ; 
  posterior 
  extremity 
  bluntly 
  pointed 
  ; 
  a 
  very 
  

   obtuse 
  angle 
  often 
  observed 
  on 
  each 
  side, 
  midway 
  between 
  the 
  

   posterior 
  terminal 
  angle 
  and 
  the 
  convexity 
  of 
  the 
  lateral 
  margin. 
  

  

  The 
  most 
  perfect 
  plate 
  I 
  have 
  seen 
  is 
  that 
  represented 
  in 
  PI. 
  vi. 
  

   fig. 
  1 
  reduced 
  more 
  than 
  one-half, 
  and 
  measures 
  10| 
  inches 
  in 
  

   length 
  by 
  6J 
  in 
  breadth, 
  but 
  among 
  the 
  imperfect 
  specimens 
  

   belonging 
  to 
  the 
  Elgin 
  Museum 
  are 
  some 
  which 
  indicated 
  consider- 
  

   ably 
  larger 
  size, 
  and 
  which 
  attained 
  a 
  thickness 
  of 
  from 
  J 
  to 
  § 
  inch. 
  

  

  The 
  internal 
  surface 
  is 
  smooth, 
  sometimes 
  showing 
  faint 
  pustular 
  

   elevations, 
  and 
  often 
  also 
  a 
  few 
  shallow 
  concentric 
  growth-furrows 
  

   parallel 
  with 
  the 
  margins 
  ; 
  it 
  is 
  formed 
  by 
  a 
  basal 
  layer 
  of 
  compact 
  

   tissue, 
  with 
  very 
  few 
  vascular 
  canals. 
  By 
  far 
  the 
  greater 
  thick- 
  

   ness 
  of 
  the 
  plate 
  is 
  formed, 
  however, 
  of 
  a 
  middle 
  layer 
  which 
  is 
  

   completely 
  permeated 
  by 
  so 
  close 
  a 
  meshwork 
  of 
  tortuous 
  vascular 
  

   canals 
  as 
  to 
  appear 
  almost 
  spongy 
  in 
  texture 
  when 
  broken 
  across. 
  

   In 
  most 
  of 
  the 
  specimens 
  the 
  third 
  or 
  outer 
  layer 
  is 
  wanting, 
  and 
  

   the 
  surface 
  of 
  the 
  exposed 
  middle 
  layer 
  is 
  seen 
  with 
  its 
  vascular 
  

   canals 
  opened 
  into, 
  much 
  as 
  in 
  a 
  cross 
  fracture. 
  This 
  outer 
  surface 
  

   of 
  the 
  middle 
  layer 
  is 
  sometimes 
  even, 
  but 
  in 
  many 
  cases 
  it 
  exhibits 
  

   an 
  arrangement 
  of 
  shallow 
  polygonal 
  depressions, 
  fitting 
  closely 
  to 
  

   each 
  other 
  like 
  the 
  cells 
  of 
  a 
  honeycomb, 
  as 
  is 
  shown 
  in 
  PI. 
  vi. 
  

  

  