﻿10 
  ACTINOPTERYGII. 
  

  

  teeth 
  ; 
  mandible 
  very 
  deep 
  posteriorly 
  ; 
  a 
  single 
  opercular 
  bone 
  

   on 
  each 
  side. 
  Head 
  and 
  opercular 
  bones 
  ornamented 
  chiefly 
  with 
  

   striations, 
  sometimes 
  reticulated 
  and 
  in 
  part 
  tuberculated. 
  Long, 
  

   slender 
  ribs 
  present. 
  Pin-rays 
  distantly 
  articulated; 
  fulcra 
  absent. 
  

   Paired 
  fins 
  small 
  ; 
  dorsal 
  and 
  anal 
  fins 
  large, 
  directly 
  opposed 
  ; 
  

   caudal 
  fin 
  truncated 
  behind, 
  symmetrical. 
  Trunk 
  with 
  four 
  longi- 
  

   tudinal 
  series 
  of 
  dermal 
  scutes, 
  one 
  dorsal 
  and 
  another 
  ventral, 
  and 
  

   a 
  pair 
  supporting 
  the 
  " 
  lateral 
  line 
  " 
  ; 
  no 
  intermediate 
  scales. 
  

  

  The 
  cranium 
  in 
  this 
  genus 
  is 
  completely 
  enveloped 
  in 
  membrane- 
  

   bones, 
  which 
  are 
  more 
  or 
  less 
  fused 
  together 
  in 
  the 
  adult 
  and 
  firmly 
  

   connected 
  at 
  the 
  side 
  in 
  advance 
  of 
  the 
  orbit 
  with 
  the 
  similarly 
  

   fused 
  cheek-plates. 
  The 
  constitution 
  of 
  the 
  cranial 
  shield 
  is 
  not 
  

   satisfactorily 
  known, 
  but 
  it 
  extends 
  backwards 
  beyond 
  the 
  skull 
  

   to 
  the 
  hinder 
  border 
  of 
  the 
  operculum. 
  The 
  parasphenoid, 
  as 
  seen 
  

   in 
  side 
  view, 
  appears 
  curved, 
  the 
  convexity 
  being 
  downwards 
  ; 
  a 
  

   short 
  and 
  broad 
  plate 
  extends 
  from 
  it 
  on 
  each 
  side 
  over 
  the 
  otic 
  

   region 
  ; 
  and 
  the 
  bone 
  is 
  also 
  prolonged 
  backwards 
  beyond 
  the 
  skull 
  

   to 
  the 
  same 
  degree 
  as 
  the 
  cranial 
  roof 
  already 
  noted. 
  The 
  orbit 
  

   is 
  large, 
  and 
  there 
  is 
  distinct 
  evidence 
  of 
  an 
  ossified 
  sclerotic, 
  or 
  at 
  

   least 
  of 
  a 
  hardened 
  sclerotic 
  ring. 
  The 
  nasal 
  opening 
  is 
  single 
  on 
  

   each 
  side, 
  and 
  obliquely 
  elongated 
  ; 
  and 
  whatever 
  appearance 
  there 
  

   may 
  be 
  of 
  a 
  second 
  smaller 
  opening 
  between 
  the 
  latter 
  and 
  the 
  

   orbit 
  in 
  certain 
  specimens, 
  must 
  be 
  regarded 
  as 
  deceptive. 
  One 
  

   long 
  posterior 
  suborbital 
  bone 
  is 
  distinct, 
  deepest 
  behind, 
  and 
  pro- 
  

   duced 
  as 
  a 
  narrow 
  bar 
  beneath 
  the 
  orbit 
  ; 
  but 
  nothing 
  further 
  is 
  

   definitely 
  known 
  concerning 
  the 
  limits 
  of 
  the 
  premaxillae, 
  maxillae, 
  

   and 
  the 
  other 
  elements 
  of 
  the 
  cheek. 
  The 
  hyomandibular 
  is 
  not 
  

   much 
  expanded 
  at 
  either 
  extremity, 
  and 
  its 
  long 
  axis 
  is 
  nearly 
  

   vertical 
  ; 
  the 
  quadrate 
  is 
  relatively 
  large 
  and 
  triangular 
  in 
  shape. 
  

   The 
  mandible 
  is 
  deepest 
  at 
  its 
  hinder 
  extremity, 
  and 
  its 
  posterior 
  

   border 
  descends 
  almost 
  vertically 
  from 
  the 
  articulation 
  with 
  the 
  

   skull. 
  The 
  angular 
  and 
  articular 
  bones 
  are 
  fused 
  together, 
  and 
  

   the 
  expanded 
  outer 
  surface 
  of 
  the 
  former 
  is 
  marked 
  by 
  radiating 
  

   branches 
  from 
  the 
  sensory 
  canal 
  which 
  traverses 
  its 
  length. 
  As 
  

   to 
  the 
  limits 
  of 
  the 
  dentary 
  and 
  splenial, 
  there 
  is 
  no 
  precise 
  in- 
  

   formation 
  ; 
  but 
  the 
  fact 
  that 
  a 
  double 
  series 
  of 
  large 
  teeth 
  extends 
  

   quite 
  to 
  the 
  termination 
  of 
  the 
  mandible, 
  suggests 
  that 
  there 
  is 
  

   no 
  presymphysial 
  bone. 
  The 
  dentition 
  on 
  the 
  margin 
  of 
  both 
  jaws 
  

   consists 
  of 
  a 
  series 
  of 
  large, 
  enamel-tipped, 
  conical 
  teeth, 
  well 
  

   spaced, 
  with 
  minute 
  intermediate 
  teeth 
  ; 
  and 
  some 
  of 
  the 
  inner 
  

   bones 
  of 
  the 
  mouth 
  are 
  also 
  provided 
  with 
  minute 
  teeth. 
  A 
  small 
  

   oval 
  operculum 
  is 
  attached 
  by 
  an 
  articulation 
  near 
  the 
  upper 
  end 
  of 
  

   its 
  anterior 
  border 
  to 
  the 
  hyomandibular 
  ; 
  but 
  there 
  is 
  no 
  evidence 
  

  

  