﻿448 
  

  

  ACTINOPTEKYOII. 
  

  

  

  smaller 
  than 
  the 
  trapezoidal 
  operculum, 
  from 
  which 
  it 
  is 
  divided 
  

   by 
  an 
  oblique 
  suture 
  ; 
  branchiostegal 
  rays 
  numerous. 
  Pleurocentra 
  

   and 
  hypocentra 
  in 
  notochordal 
  sheath 
  fused 
  or 
  separate. 
  Fin-fulcra 
  

   small, 
  extendiug 
  along 
  the 
  foremost 
  ray 
  of 
  each 
  of 
  the 
  fins. 
  Pectoral 
  

   not 
  excessively 
  large, 
  but 
  much 
  exceeding 
  the 
  pelvic 
  fins 
  in 
  size 
  ; 
  

   dorsal 
  and 
  anal 
  fins 
  triangular 
  in 
  shape, 
  not 
  extended, 
  the 
  former 
  

   opposite 
  or 
  arising 
  somewhat 
  behind 
  the 
  pelvic 
  fins; 
  caudal 
  fin 
  

   deeply 
  forked. 
  Scales 
  thin, 
  deeply 
  overlapping, 
  usually 
  with 
  an 
  

   inner 
  rib 
  and 
  peg-and-socket 
  articulation, 
  and 
  the 
  external 
  layer 
  of 
  

   ganoine 
  smooth 
  or 
  feebly 
  ornamented 
  ; 
  principal 
  flank-scales 
  deeper 
  

   than 
  broad, 
  ventral 
  scales 
  in 
  part 
  broader 
  than 
  deep 
  ; 
  no 
  enlarged 
  

   series 
  of 
  ridge-scales, 
  but 
  a 
  large 
  scale 
  at 
  the 
  base 
  of 
  one 
  or 
  both 
  

   lobes 
  of 
  the 
  caudal 
  fin, 
  and 
  three 
  slightly 
  enlarged 
  scales 
  round 
  the 
  

   anus 
  at 
  the 
  base 
  of 
  the 
  anal 
  fin. 
  Lateral 
  line 
  opening 
  by 
  widely 
  

   separated 
  large 
  pores. 
  

  

  Little 
  can 
  be 
  added 
  to 
  the 
  osteological 
  characters 
  of 
  this 
  fish 
  

   noted 
  in 
  the 
  generic 
  diagnosis. 
  In 
  the 
  axial 
  skeleton 
  of 
  the 
  trunk 
  

   the 
  pleurocentra 
  and 
  hypocentra 
  are 
  delicate, 
  always 
  directly 
  

  

  Fig. 
  44. 
  

  

  Head, 
  etc., 
  of 
  Pholidophorus 
  macrocephalus, 
  left 
  lateral 
  aspect 
  (after 
  Zittel). 
  

   cl., 
  clavicle 
  ; 
  fr., 
  frontal 
  ; 
  i.op., 
  interoperculum 
  ; 
  md., 
  mandible 
  ; 
  mx., 
  maxilla 
  ; 
  

   net., 
  nasal 
  ; 
  op., 
  operculum 
  ; 
  pa., 
  parietal 
  ; 
  pmx., 
  premaxilla 
  ; 
  pop., 
  pre- 
  

   operculum 
  ; 
  psph., 
  parasphenoid 
  ; 
  pt, 
  supratemporal 
  ; 
  scl., 
  " 
  supraclavicle 
  " 
  

   (? 
  post-temporal) 
  ; 
  so., 
  suborbital 
  ; 
  sop., 
  suboperculum. 
  

  

  opposed, 
  not 
  alternating 
  ; 
  but 
  it 
  is 
  difficult 
  to 
  determine 
  whether 
  or 
  

   not 
  they 
  usually 
  fuse 
  into 
  complete 
  rings. 
  In 
  the 
  abdominal 
  region, 
  

   the 
  two 
  halves 
  of 
  each 
  neural 
  arch 
  appear 
  to 
  be 
  separate 
  from 
  each 
  

   other 
  and 
  from 
  the 
  spine 
  they 
  support 
  ; 
  while 
  the 
  ribs 
  are 
  delicate 
  

   and 
  extend 
  only 
  about 
  half-way 
  to 
  the 
  ventral 
  border. 
  The 
  remote 
  

   situation 
  of 
  the 
  anus 
  is 
  indicated 
  not 
  merely 
  by 
  the 
  enlarged 
  median 
  

   and 
  paired 
  scales 
  surrounding 
  it, 
  but 
  also 
  by 
  coprolitic 
  matter 
  in 
  

  

  