﻿40 
  Mr. 
  R. 
  Lydekker 
  on 
  the 
  

  

  not 
  widely 
  differ 
  from 
  that 
  of 
  Podica 
  ; 
  the 
  lateral 
  margins 
  

   are 
  more 
  concave, 
  since 
  the 
  lateral 
  processes 
  jut 
  out 
  at 
  a 
  

   larger 
  angle 
  with 
  the 
  median 
  axis. 
  These 
  processes, 
  moreover, 
  

   do 
  not 
  extend 
  beyond 
  the 
  posterior 
  margin 
  of 
  the 
  sternum. 
  

   The 
  sternum 
  also 
  is 
  shorter 
  in 
  proportion 
  to 
  its 
  length 
  in 
  

   the 
  American 
  than 
  in 
  the 
  African 
  Fin-foot. 
  

  

  The 
  measurements 
  of 
  the 
  sternum 
  of 
  Heliorms 
  are 
  as 
  

   follows 
  : 
  — 
  Length 
  35 
  mm. 
  ; 
  least 
  breadth 
  16 
  mm. 
  

  

  With 
  these 
  measurements 
  may 
  be 
  compared 
  those 
  of 
  

   Podica 
  : 
  — 
  Length 
  68 
  mm. 
  ; 
  least 
  breadth 
  20 
  mm. 
  

  

  The 
  median 
  interclavicular 
  piece 
  of 
  the 
  merrythought 
  is 
  

   not 
  prolonged 
  forwards, 
  as 
  it 
  is 
  in 
  Podica. 
  

  

  VL 
  Pelvis. 
  

  

  There 
  are 
  hardly 
  any 
  points 
  of 
  difference 
  between 
  the 
  

   pelvis 
  of 
  Heliornis 
  and 
  Podica. 
  All 
  the 
  characteristic 
  

   features 
  of 
  this 
  part 
  of 
  the 
  skeleton 
  as 
  described 
  in 
  Podica 
  

   exist 
  in 
  Helio7'nis. 
  The 
  ridges 
  on 
  the 
  ischia 
  are, 
  however, 
  

   less 
  conspicuous 
  in 
  the 
  American 
  Fin-foot. 
  

  

  I 
  have 
  already 
  compared 
  the 
  ribs 
  and 
  vertehrcs 
  of 
  these 
  two 
  

   birds, 
  and 
  need 
  not 
  recapitulate 
  here 
  what 
  has 
  been 
  said 
  in 
  

   my 
  paper 
  in 
  the 
  P. 
  Z. 
  S. 
  {t. 
  c). 
  

  

  III. 
  — 
  On 
  the 
  Extinct 
  Giant 
  Birds 
  of 
  Argentina. 
  

   By 
  R. 
  Lydekker. 
  

  

  For 
  the 
  last 
  few 
  years 
  the 
  palseontological 
  world 
  has 
  been 
  

   flooded 
  with 
  accounts 
  of 
  the 
  wonderful 
  discoveries 
  of 
  mam- 
  

   malian 
  remains 
  belonging 
  to 
  new 
  or 
  little 
  known 
  types 
  

   which 
  have 
  been 
  made 
  in 
  the 
  Tertiary 
  deposits 
  of 
  Argentina. 
  

   These 
  discoveries 
  have 
  rendered 
  it 
  certain 
  that, 
  instead 
  of 
  

   having 
  to 
  do 
  merely 
  with 
  a 
  single 
  fauna 
  of 
  Pleistocene 
  age, 
  we 
  

   have 
  there 
  laid 
  before 
  us 
  a 
  whole 
  series 
  of 
  faunas, 
  which 
  evi- 
  

   dently 
  occupied 
  a 
  considerable 
  portion 
  of 
  the 
  Tertiary 
  period. 
  

   The 
  geologists 
  and 
  palaeontologists 
  of 
  Argentina 
  are, 
  indeed, 
  

   of 
  opinion 
  that 
  the 
  deposits 
  yielding 
  vertebrate 
  remains 
  are 
  

   equivalent 
  to 
  the 
  whole 
  of 
  the 
  European 
  Tertiary 
  series, 
  from 
  

  

  