﻿EUGNATHIDJE. 
  

  

  287 
  

  

  more 
  than 
  one 
  series 
  over 
  the 
  whole 
  of 
  the 
  splenial 
  ; 
  preoperculum 
  

   smooth 
  and 
  narrow 
  ; 
  suboperculum 
  of 
  moderate 
  size, 
  about 
  half 
  as 
  

   large 
  as 
  the 
  nearly 
  rectangular 
  operculum, 
  and 
  with 
  a 
  short 
  

   ascending 
  process 
  at 
  its 
  antero-superior 
  angle. 
  Ossifications 
  in 
  the 
  

   sheath 
  of 
  the 
  notochord 
  observed 
  only 
  in 
  the 
  largest 
  species 
  ; 
  

   ossified 
  ribs 
  slender. 
  Fulcra 
  biserial, 
  well-developed 
  on 
  all 
  the 
  fins 
  

   except 
  the 
  pectorals, 
  on 
  which 
  they 
  are 
  feeble. 
  Pectoral 
  much 
  

   exceeding 
  the 
  pelvic 
  fins 
  in 
  size, 
  but 
  the 
  latter 
  well-developed 
  ; 
  

   dorsal 
  and 
  anal 
  fins 
  triangular 
  in 
  shape, 
  the 
  former 
  arising 
  opposite 
  

   or 
  immediately 
  behind 
  the 
  pelvic 
  fins 
  ; 
  caudal 
  fin 
  forked. 
  Scales 
  

   thick, 
  with 
  a 
  narrow 
  overlapped 
  border, 
  an 
  inner 
  rib, 
  and 
  a 
  feeble 
  

   peg-and-socket 
  articulation 
  ; 
  superficial 
  ganoine 
  smooth 
  on 
  the 
  

   anterior 
  half 
  of 
  each 
  scale, 
  passing 
  on 
  part 
  of 
  the 
  body 
  into 
  trans- 
  

   verse 
  rugae 
  and 
  crenulations 
  posteriorly; 
  principal 
  flank-scales 
  

   rarely, 
  and 
  then 
  only 
  in 
  part, 
  deeper 
  than 
  broad, 
  several 
  series 
  of 
  

   ventral 
  scales 
  much 
  broader 
  than 
  deep 
  ; 
  postclavicular 
  scales 
  large 
  ; 
  

   no 
  enlarged 
  scales 
  on 
  the 
  dorsal 
  ridge 
  or 
  in 
  the 
  region 
  of 
  the 
  anus. 
  

   Lateral 
  line 
  inconspicuous. 
  

  

  A 
  description 
  of 
  the 
  skeleton 
  of 
  Eugnathus 
  will 
  equally 
  apply 
  to 
  

   Heterolejpidotus 
  (see 
  p. 
  304), 
  which 
  differs 
  only 
  in 
  minor 
  particulars. 
  

   The 
  chondrocranium 
  is 
  well 
  ossified, 
  and 
  the 
  basicranial 
  axis 
  is 
  

   straight. 
  The 
  basioccipital 
  exhibits 
  on 
  its 
  posterior 
  face 
  a 
  deep 
  

   conical 
  fossa 
  for 
  the 
  notochord 
  ; 
  and 
  the 
  inferior 
  aspect 
  of 
  the 
  bone 
  

   is 
  marked 
  by 
  a 
  slight 
  longitudinal 
  groove, 
  though 
  there 
  is 
  apparently 
  

   no 
  basicranial 
  canal. 
  A 
  robust 
  ossification 
  is 
  conspicuous 
  both 
  in 
  

   the 
  postfrontal 
  and 
  in 
  the 
  prefrontal 
  region. 
  Nearly 
  the 
  whole 
  of 
  

   the 
  base 
  of 
  the 
  skull 
  is 
  sheathed 
  by 
  a 
  large 
  parasphenoid, 
  which 
  

   appears 
  to 
  terminate 
  in 
  advance 
  of 
  the 
  occiput 
  and 
  exhibits 
  a 
  pair 
  

   of 
  long 
  basipterygoid 
  processes. 
  In 
  front 
  of 
  the 
  latter 
  the 
  para- 
  

   sphenoid 
  bears 
  a 
  long, 
  lenticular 
  patch 
  of 
  minute 
  granular 
  teeth. 
  

   The 
  vomers 
  are 
  unsatisfactorily 
  known, 
  but 
  a 
  cluster 
  of 
  larger 
  short 
  

   and 
  conical 
  teeth 
  appears 
  to 
  belong 
  to 
  them 
  : 
  they 
  are 
  certainly 
  

   paired 
  in 
  Heterolepidotus. 
  The 
  membrane 
  bones 
  of 
  the 
  cranial 
  roof 
  

   form 
  a 
  continuous 
  shield, 
  which 
  is 
  nearly 
  flat. 
  The 
  parietals 
  

   are 
  small 
  and 
  short, 
  meeting 
  in 
  a 
  remarkably 
  wavy 
  suture 
  which 
  

   makes 
  them 
  an 
  unsymmetrical 
  pair. 
  These 
  are 
  flanked 
  by 
  the 
  

   squamosals, 
  which 
  are 
  somewhat 
  longer 
  and 
  form 
  the 
  postero- 
  

   lateral 
  angles 
  of 
  the 
  cranial 
  roof. 
  The 
  frontals 
  are 
  very 
  large, 
  

   broad 
  behind 
  but 
  attenuated 
  in 
  front; 
  and 
  the 
  median 
  suture 
  

   between 
  them 
  is 
  more 
  or 
  less 
  wavy 
  in 
  its 
  hinder 
  portion. 
  The 
  

   postfrontal 
  is 
  exposed 
  at 
  the 
  anterior 
  end 
  of 
  the 
  squamosal, 
  and 
  

   between 
  it 
  and 
  the 
  prefrontal 
  there 
  extends 
  a 
  series 
  of 
  about 
  three 
  

   supraorbital 
  plates. 
  The 
  cheek 
  is 
  completely 
  covered 
  with 
  thin 
  

  

  