﻿4 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.96 
  

  

  geoffroyi 
  group, 
  meets 
  or 
  closely 
  approaches 
  the 
  range 
  of 
  the 
  nearly 
  all 
  

   black 
  Tohustus. 
  The 
  Rio 
  Amazonas, 
  however, 
  seems 
  to 
  be 
  an 
  effective 
  

   barrier 
  separating 
  the 
  ranges 
  of 
  A. 
  paniscus 
  paniscus 
  and 
  A. 
  helzebuth 
  

   marginatiis. 
  

  

  Several 
  large 
  series 
  of 
  specimens 
  from 
  the 
  same 
  locality 
  have 
  

   afforded 
  us 
  much 
  information 
  concerning 
  the 
  range 
  of 
  individual 
  

   variation 
  that 
  may 
  be 
  expected 
  in 
  the 
  genus 
  Ateles. 
  The 
  thumb 
  is 
  

   normally 
  represented 
  by 
  a 
  short 
  metacarpal, 
  which 
  ordinarily 
  is 
  not 
  

   visible 
  externally. 
  When, 
  in 
  occasional 
  individuals, 
  a 
  short 
  proximal 
  

   phalanx 
  is 
  retained 
  it 
  constitutes 
  the 
  vestigial 
  nailless 
  thumb. 
  In 
  

   two 
  specimens 
  of 
  velleroms 
  (U. 
  S. 
  N. 
  M. 
  Nos. 
  74662, 
  74663) 
  from 
  

   Santa 
  Efigenia, 
  Oaxaca, 
  and 
  in 
  one 
  of 
  the 
  same 
  form 
  (A. 
  M. 
  N. 
  H. 
  

   IS'o. 
  123282) 
  from 
  Cantoral, 
  Honduras, 
  these 
  thumbs 
  are 
  present 
  on 
  

   one 
  hand 
  and 
  not 
  on 
  the 
  other. 
  In 
  one 
  of 
  pananiensis 
  (A. 
  M. 
  N. 
  H. 
  

   No. 
  141980) 
  from 
  Canas 
  Gordas, 
  Costa 
  Rica, 
  the 
  thumbs 
  are 
  present 
  

   on 
  both 
  hands. 
  In 
  a 
  specimen 
  of 
  hyhridus 
  from 
  Guaimaral, 
  Colom- 
  

   bia, 
  vestigial 
  thumbs 
  on 
  both 
  hands 
  bear 
  small 
  nails. 
  Lonnberg 
  

   (Arkiv 
  for 
  Zool., 
  vol. 
  32A, 
  No. 
  25, 
  p. 
  8, 
  July 
  18, 
  1940) 
  describes 
  a 
  

   well-developed 
  thumb 
  with 
  a 
  well-developed 
  nail 
  on 
  one 
  hand 
  only 
  

   in 
  a 
  specimen 
  of 
  paniscus^ 
  a 
  small 
  thumb 
  present 
  on 
  the 
  other 
  hand 
  

   being 
  nailless. 
  All 
  three 
  specimens 
  of 
  paniscus 
  (A. 
  M. 
  N. 
  H. 
  Nos. 
  

   94134, 
  94135, 
  94136) 
  from 
  Rio 
  Jamunda, 
  near 
  Faro, 
  on 
  the 
  north 
  bank 
  

   of 
  the 
  Rio 
  Amazonas, 
  have 
  thumbs 
  on 
  both 
  hands, 
  as 
  already 
  re- 
  

   corded 
  by 
  Tate 
  (Bull. 
  Amer. 
  Mus. 
  Nat. 
  Hist., 
  vol. 
  76, 
  p. 
  215, 
  Oct. 
  20, 
  

   1939). 
  Two 
  others 
  from 
  Lago 
  Cuipeua, 
  farther 
  east 
  on 
  the 
  same 
  

   bank 
  of 
  this 
  river, 
  however, 
  are 
  thumbless. 
  Lonnberg 
  (op. 
  cit.) 
  

   refers 
  to 
  the 
  absence 
  of 
  thumbs 
  in 
  specimens 
  of 
  Ateles 
  ater 
  

   [= 
  chameh] 
  from 
  various 
  localities, 
  but 
  they 
  are 
  present 
  on 
  both 
  

   hands 
  in 
  a 
  skin 
  (C. 
  M. 
  No. 
  2775) 
  from 
  Rio 
  Yapacani, 
  Santa 
  Cruz, 
  

   Bolivia. 
  The 
  evidence 
  thus 
  presented 
  indicates 
  that 
  vestigial 
  thumbs 
  

   occur 
  irregularly 
  throughout 
  the 
  genus, 
  and 
  no 
  specific 
  significance 
  

   is 
  attached 
  to 
  their 
  presence 
  or 
  absence. 
  

  

  Certain 
  cranial 
  details 
  believed 
  by 
  some 
  authors 
  to 
  represent 
  dis- 
  

   tinctive 
  characters 
  prove 
  to 
  be 
  too 
  variable 
  to 
  be 
  of 
  much 
  value. 
  As 
  

   Lonnberg 
  [op. 
  cit.) 
  has 
  pointed 
  out, 
  some 
  of 
  the 
  features 
  mentioned 
  

   as 
  characters 
  by 
  Tate 
  {op. 
  cit.) 
  in 
  comparing 
  species 
  are 
  subject 
  to 
  

   a 
  wide 
  range 
  of 
  variation. 
  The 
  antorbital 
  or 
  "malar 
  foramen" 
  varies 
  

   from 
  one 
  or 
  two 
  "pin-holes" 
  to 
  rounded 
  openings 
  5 
  mm. 
  in 
  diameter 
  

   through 
  the 
  jugal. 
  These 
  often 
  differ 
  in 
  size 
  and 
  number 
  on 
  the 
  

   two 
  sides 
  of 
  the 
  same 
  skull. 
  Tate 
  also 
  refers 
  to 
  "small, 
  triangular 
  

   pterygoids 
  without 
  pointed 
  tips" 
  as 
  a 
  cranial 
  character 
  in 
  paniscus. 
  

   In 
  the 
  Cebidae 
  the 
  fossae 
  between 
  the 
  true 
  pterygoids 
  and 
  their 
  ex- 
  

   ternal 
  reduplications 
  are 
  large 
  and 
  deep 
  in 
  Cehus., 
  reduced 
  to 
  a 
  ves- 
  

   tige 
  in 
  Alouatta., 
  and 
  entirely 
  wanting 
  in 
  Ateles. 
  The 
  external 
  

   reduplications 
  of 
  the 
  pterygoids 
  have 
  the 
  tips 
  broken 
  off 
  in 
  the 
  

  

  