﻿SEMIONOTmE. 
  

  

  143 
  

  

  A 
  species 
  equalling 
  D. 
  politus 
  in 
  size. 
  Maximum 
  depth 
  of 
  trunk 
  

   somewhat 
  less 
  than 
  its 
  length 
  (exclusive 
  of 
  the 
  caudal 
  fin) 
  and 
  a 
  

   little 
  more 
  than 
  three 
  times 
  as 
  great 
  as 
  the 
  depth 
  of 
  the 
  caudal 
  

   pedicle. 
  Head 
  with 
  opercular 
  apparatus 
  occupying 
  nearly 
  one- 
  

   quarter 
  of 
  the 
  total 
  length 
  of 
  the 
  fish 
  ; 
  the 
  external 
  hones 
  orna- 
  

   mented 
  with 
  rounded, 
  sharply 
  defined 
  tuberculations 
  of 
  moderate 
  

   size, 
  sometimes 
  elongated, 
  rarely 
  fused 
  into 
  short 
  rugae. 
  Marginal 
  

   teeth 
  large 
  and 
  unicuspid. 
  Scales 
  smooth, 
  with 
  few 
  sparse 
  punc- 
  

   tations; 
  the 
  hinder 
  border 
  delicately 
  serrated, 
  the 
  serrations 
  

   becoming 
  especially 
  conspicuous 
  in 
  the 
  middle 
  of 
  the 
  caudal 
  region. 
  

  

  The 
  form 
  of 
  the 
  operculum 
  is 
  apparently 
  not 
  constant, 
  but 
  in 
  

   most 
  of 
  the 
  specimens 
  assigned 
  to 
  D. 
  punctatus 
  it 
  is 
  relatively 
  

   narrower 
  and 
  deeper 
  than 
  in 
  the 
  type 
  species. 
  

  

  Form, 
  fy 
  Loo. 
  Lower 
  Lias 
  : 
  Dorsetshire. 
  Upper 
  Lias 
  : 
  Wiirtem- 
  

   berg. 
  

  

  Unless 
  otherwise 
  stated, 
  the 
  following 
  specimens 
  were 
  all 
  obtained 
  

   from 
  the 
  neighbourhood 
  of 
  Lyme 
  Regis 
  : 
  — 
  

  

  19486. 
  Imperfect 
  head 
  and 
  trunk, 
  wanting 
  the 
  greater 
  part 
  of 
  the 
  

   fins, 
  but 
  displaying 
  the 
  squamation. 
  Purchased, 
  1845. 
  

  

  35793. 
  Well-preserved 
  fish 
  with 
  imperfect 
  fins. 
  The 
  operculum 
  

   measures 
  0*045 
  in 
  maximum 
  depth 
  and 
  0*03 
  in 
  maximum 
  

   width 
  : 
  the 
  upper 
  end 
  is 
  arched 
  forwards, 
  rounded, 
  and 
  

   tapering, 
  and 
  many 
  of 
  the 
  superficial 
  tuberculations 
  are 
  

   elongated. 
  Purchased, 
  1860. 
  

  

  36258. 
  Another 
  fine 
  specimen 
  relatively 
  more 
  elongated 
  (apparently 
  

   by 
  distortion). 
  The 
  operculum 
  is 
  less 
  deep 
  in 
  proportion 
  

   to 
  its 
  breadth 
  than 
  in 
  no. 
  35793, 
  and 
  there 
  is 
  more 
  ten- 
  

   dency 
  to 
  the 
  elongation 
  of 
  the 
  superficial 
  tuberculations. 
  

   The 
  tubercles 
  upon 
  the 
  cranial 
  roof 
  exhibit 
  frequent 
  fusion 
  

   into 
  continuous 
  series. 
  Purchased, 
  1862. 
  

  

  P. 
  3554. 
  Nearly 
  complete 
  fish 
  0*39 
  in 
  length, 
  with 
  an 
  operculum 
  

   of 
  the 
  same 
  form 
  as 
  no. 
  35793, 
  more 
  sparsely 
  tuber- 
  

   culated. 
  The 
  marginal 
  teeth 
  are 
  unicuspid, 
  and 
  very 
  

   long 
  though 
  robust. 
  The 
  scales 
  of 
  the 
  lateral 
  line 
  exhibit 
  

   crescentic 
  perforations 
  ; 
  and 
  there 
  are 
  traces 
  of 
  a 
  superior 
  

   lateral 
  sensory 
  canal, 
  not 
  perforating 
  the 
  scales 
  it 
  traverses, 
  

   but 
  passing 
  through 
  pairs 
  of 
  elongated 
  tubercles. 
  

  

  Enniskillen 
  Coll, 
  

  

  P. 
  2053. 
  Imperfect 
  large 
  specimen 
  in 
  septarian 
  nodule, 
  labelled 
  

   Tetragonolepis 
  leachi 
  by 
  Agassiz. 
  Egerton 
  Coll. 
  

  

  