﻿318 
  ACTItfOPTERYGII. 
  

  

  Type. 
  Imperfectly 
  preserved 
  fish 
  ; 
  British 
  Museum. 
  

  

  The 
  type 
  species, 
  attaining 
  a 
  length 
  of 
  about 
  0*35. 
  Length 
  of 
  

   head 
  with 
  opercular 
  apparatus 
  equalling 
  the 
  maximum 
  depth 
  of 
  the 
  

   trunk 
  and 
  nearly 
  one-quarter 
  of 
  the 
  total 
  length 
  of 
  the 
  fish. 
  The 
  

   ridged 
  ornament 
  of 
  the 
  head 
  coarse, 
  very 
  rarely 
  mingled 
  with 
  few 
  

   tubercles, 
  and 
  covering 
  all 
  the 
  external 
  bones 
  except 
  the 
  gular 
  

   plate 
  and 
  branchiostegal 
  rays, 
  which 
  are 
  nearly 
  smooth 
  • 
  the 
  supra- 
  

   clavicle 
  also 
  ornamented 
  with 
  finer 
  transverse 
  ridges. 
  Most 
  of 
  the 
  

   ridges 
  on 
  the 
  cranium, 
  cheeks, 
  and 
  opercular 
  bones 
  longitudinal 
  ; 
  

   the 
  ridges 
  on 
  the 
  upper 
  portion 
  of 
  the 
  dentary 
  and 
  hinder 
  half 
  of 
  

   maxilla 
  oblique. 
  The 
  stouter 
  fin-rays 
  ornamented 
  with 
  few 
  fine 
  

   longitudinal 
  ridges 
  of 
  ganoine 
  ; 
  pelvic 
  fins 
  arising 
  midway 
  between 
  

   the 
  pectorals 
  and 
  the 
  caudal 
  ; 
  dorsal 
  fin 
  with 
  slightly 
  more 
  than 
  

   20 
  rays, 
  arising 
  well 
  in 
  advance 
  of 
  the 
  pelvic 
  pair. 
  Scales 
  marked 
  

   with 
  from 
  one 
  to 
  four 
  or 
  five 
  delicate, 
  irregular, 
  longitudinal 
  furrows, 
  

   sometimes 
  discontinuous, 
  sometimes 
  branching, 
  rarely 
  reaching 
  the 
  

   hinder 
  border 
  except 
  on 
  the 
  middle 
  of 
  the 
  abdominal 
  flank, 
  and 
  

   producing 
  an 
  ornament 
  of 
  large, 
  incomplete, 
  rounded 
  ridges 
  ; 
  the 
  

   hinder 
  border 
  deeply 
  and 
  coarsely 
  denticulated. 
  

  

  Form. 
  <$f 
  Log. 
  Upper 
  Lias 
  : 
  Yorkshire, 
  Wiirtemberg, 
  and 
  Yonne, 
  

   France. 
  

  

  P. 
  3688. 
  A 
  much 
  crushed 
  and 
  distorted 
  fish 
  described 
  and 
  figured 
  

   by 
  Agassiz, 
  op. 
  cit. 
  1844, 
  to 
  be 
  regarded 
  as 
  the 
  type 
  

   specimen 
  ; 
  Whitby, 
  Yorkshire. 
  One 
  of 
  the 
  pelvic 
  fins 
  is 
  

   mistaken 
  in 
  the 
  original 
  description 
  for 
  the 
  anal 
  ; 
  and 
  the 
  

   obscure 
  caudal 
  extremity, 
  with 
  traces 
  of 
  the 
  caudal 
  fin, 
  is 
  

   very 
  inaccurately 
  drawn. 
  The 
  appearance 
  of 
  teeth 
  in 
  the 
  

   mandible 
  is 
  deceptive. 
  EnnisTcillen 
  Coll. 
  

  

  P. 
  858-a. 
  Two 
  imperfect 
  specimens 
  displaying 
  some 
  of 
  the 
  head- 
  

   bones 
  and 
  the 
  greater 
  part 
  of 
  the 
  squamation 
  ; 
  Whitby. 
  

   The 
  first 
  specimen 
  exhibits 
  the 
  gaping 
  mouth, 
  but 
  no 
  

   teeth 
  ; 
  and 
  portions 
  of 
  all 
  the 
  fins 
  except 
  the 
  anal 
  are 
  

   preserved. 
  The 
  second 
  specimen 
  is 
  more 
  imperfect, 
  but 
  

   shows 
  remains 
  of 
  the 
  smooth 
  branchiostegals 
  and 
  gular 
  

   plate. 
  Egerton 
  Coll. 
  

  

  P. 
  3691. 
  Remains 
  of 
  the 
  hinder 
  portion 
  of 
  the 
  head 
  and 
  the 
  

   imperfectly 
  preserved 
  trunk 
  of 
  a 
  large 
  fish, 
  labelled 
  by 
  

   Agassiz 
  ; 
  Whitby. 
  Enniskillen 
  Coll. 
  

  

  P. 
  5222. 
  Imperfect 
  head 
  and 
  ventral 
  aspect 
  of 
  the 
  abdominal 
  region 
  

   of 
  a 
  fish 
  preserved 
  in 
  a 
  nodule 
  ; 
  Whitby. 
  The 
  bases 
  of 
  a 
  

   single 
  regular 
  series 
  of 
  small 
  teeth 
  are 
  exhibited 
  on 
  the 
  

  

  