﻿16 
  JOURNAL 
  OF 
  the; 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOI.. 
  12, 
  NO. 
  1 
  

  

  longer. 
  It 
  is 
  firmly 
  attached 
  to 
  the 
  base 
  of 
  the 
  exoccipital 
  by 
  tough 
  

   connective 
  tissue. 
  

  

  The 
  pectoral 
  girdle 
  is 
  further 
  attached 
  to 
  the 
  skull 
  and 
  vertebrae 
  

   by 
  three 
  rod-like 
  ligaments 
  on 
  each 
  side. 
  The 
  upper 
  ligament 
  passes 
  

   from 
  the 
  posttemporal 
  to 
  the 
  basioccipital. 
  The 
  second 
  is 
  attached 
  

   to 
  the 
  supraclavical 
  and 
  the 
  first 
  vertebra 
  which 
  is 
  ankylosed 
  with 
  

   the 
  skull. 
  The 
  third 
  ligament 
  attaches 
  the 
  clavical 
  to 
  the 
  second 
  

   vertebra, 
  or 
  the 
  first 
  which 
  is 
  not 
  ankylosed 
  with 
  the 
  skull. 
  

  

  Scales. 
  — 
  The 
  scales 
  of 
  Argentina 
  silus 
  differ 
  greatly 
  from 
  those 
  of 
  

   Osmeridae 
  or 
  Salmonidae. 
  In 
  these 
  two 
  families, 
  the 
  scales 
  are 
  smooth 
  

   and 
  cycloid, 
  but 
  in 
  Argentina 
  silus 
  they 
  are 
  roughened 
  by 
  small 
  spines, 
  

   and 
  they 
  are 
  ctenoid 
  in 
  a 
  manner 
  similar 
  to 
  certain 
  clupeids 
  and 
  

   percids 
  (Menhaden 
  and 
  Stizostedion) 
  . 
  The 
  heart-shaped 
  scales 
  as 
  

   described 
  by 
  Smitt 
  appear 
  only 
  along 
  the 
  lateral 
  line. 
  

  

  SUMMARY 
  OF 
  CHARACTERISTICS 
  OF 
  Argentinidae 
  as 
  INDICATED 
  BY 
  

  

  Argentina 
  silus 
  

  

  Visceral 
  characteristics 
  

  

  Stomach 
  bluntly 
  caecal; 
  intestine 
  with 
  well-developed 
  spiral 
  valve; 
  

   pyloric 
  caeca 
  much 
  less 
  numerous 
  than 
  in 
  Coregonidae, 
  not 
  much 
  

   less 
  numerous 
  than 
  in 
  Salmonidae, 
  and 
  much 
  more 
  numerous 
  than 
  

   in 
  Osmeridae; 
  air 
  bladder 
  thick 
  and 
  silvery; 
  pneumatic 
  duct, 
  if 
  any, 
  

   connected 
  with 
  its 
  posterior 
  end. 
  

  

  Skeletal 
  characteristics 
  

  

  Cranium: 
  — 
  Frontals 
  extend 
  backward 
  overlapping 
  parietals, 
  nearly 
  

   covering 
  them. 
  Parietals 
  overlapping 
  on 
  top 
  of 
  supraoccipital 
  ; 
  

   opisthotic 
  present; 
  splenial 
  bone 
  present 
  in 
  lower 
  jaw; 
  mesopterygoids 
  

   and 
  jaws 
  toothless; 
  no 
  supplementary 
  maxillary. 
  

  

  Vertebrae: 
  — 
  66 
  all 
  told. 
  Double 
  neural 
  spines 
  in 
  first 
  21, 
  canal 
  

   being 
  open 
  in 
  first 
  20. 
  Ribs 
  on 
  all 
  but 
  last 
  three 
  abdominal 
  vertebrae. 
  

   Osseous 
  epipleurals 
  on 
  at 
  least 
  26 
  abdominal 
  vertebrae; 
  these 
  are 
  

   ankylosed 
  to 
  zygapophyses 
  and 
  neural 
  spines 
  ; 
  haemapophyses 
  of 
  

   abdominal 
  vertebrae 
  bridged 
  by 
  arch 
  instead 
  of 
  straight-edged 
  piece 
  

   as 
  in 
  Salmo; 
  pelvic 
  bones 
  with 
  trapezoidal 
  instead 
  of 
  a 
  triangular 
  

   basipterygium. 
  

  

  Pectoral 
  girdle: 
  — 
  With 
  no 
  postclavical 
  process 
  and 
  with 
  thin 
  acti- 
  

   nosts 
  which 
  are 
  connected 
  by 
  webs 
  of 
  thin 
  bone. 
  

  

  