﻿398 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.98 
  

  

  of 
  dorsal 
  wall 
  of 
  hyoid 
  bone. 
  Each 
  corner 
  of 
  tentorium 
  projected 
  

   into 
  a 
  broad 
  cornu 
  for 
  connection 
  with 
  thyreohyal. 
  Near 
  each 
  lower 
  

   corner 
  of 
  opening 
  a 
  well-developed 
  corniculum 
  for 
  attachment 
  of 
  

   stylohyoid 
  ligament 
  is 
  present. 
  Inner 
  surface 
  of 
  bone 
  smooth, 
  un- 
  

   marked 
  by 
  the 
  ridges, 
  or 
  trabeculae 
  characteristic 
  of 
  male 
  hyoid 
  of 
  

   seniculus. 
  

  

  Resemblance 
  between 
  male 
  and 
  female 
  hyoids 
  of 
  A. 
  palliata 
  is 
  much 
  

   greater 
  than 
  that 
  between 
  hyoids 
  of 
  the 
  two 
  sexes 
  of 
  A. 
  seniculus. 
  

   Nevertheless, 
  in 
  both 
  species 
  relationship 
  between 
  sexes 
  in 
  size 
  of 
  

   hyoid 
  bones 
  is 
  about 
  the 
  same. 
  Greatest 
  width 
  and 
  depth 
  of 
  one 
  

   female 
  palliata 
  hyoid, 
  14 
  by 
  27 
  mm.; 
  simple 
  tentorial 
  plate 
  less 
  de- 
  

   veloped 
  than 
  in 
  male 
  hyoid, 
  its 
  superior 
  margin 
  concave; 
  cornicules 
  

   prominent 
  but 
  only 
  slightly 
  projecting, 
  bulla 
  more 
  saclike, 
  opening 
  

   less 
  flaring 
  than 
  in 
  male 
  hyoid. 
  

  

  OTHER 
  SPECIES 
  OF 
  HOWLERS 
  

  

  Figures 
  56, 
  57 
  

  

  Hyoids 
  of 
  A. 
  helzehul 
  and 
  A.fusca 
  resemble 
  that 
  of 
  A. 
  seniculus 
  but 
  

   are 
  less 
  specialized. 
  The 
  figure 
  of 
  a 
  male 
  hyoid 
  bone 
  of 
  A. 
  beniensis 
  

   Lonnberg 
  (1941, 
  pi. 
  3, 
  figs, 
  6a-b), 
  does 
  not 
  reveal 
  important 
  difi'erences 
  

   by 
  which 
  it 
  can 
  be 
  distinguished 
  from 
  hyoids 
  of 
  the 
  seniculus 
  type. 
  

   The 
  described 
  external 
  and 
  cranial 
  characters 
  of 
  beniensis 
  indicate 
  

   that 
  it 
  may 
  best 
  be 
  regarded 
  as 
  a 
  subspecies 
  of 
  A.fusca. 
  Similarly, 
  

   A. 
  nigerrima 
  Lonnberg 
  (op. 
  cit., 
  p. 
  33), 
  judged 
  by 
  external 
  and 
  cranial 
  

   characters 
  of 
  two 
  females 
  from 
  Lago 
  do 
  Baptista, 
  east 
  side 
  of 
  the 
  lower 
  

   Rio 
  Madeira, 
  appear 
  to 
  represent 
  a 
  wholly 
  black 
  race 
  of 
  A. 
  belzebul. 
  

   The 
  hyoid 
  bones 
  of 
  both 
  females 
  are 
  available 
  and 
  show 
  agreement 
  in 
  

   important 
  characters 
  with 
  that 
  of 
  a 
  male 
  hyoid 
  of 
  A. 
  belzebul 
  from 
  

   Ilha 
  de 
  Maraj6. 
  The 
  hyoid 
  bone 
  of 
  A. 
  caraya 
  differs 
  considerably 
  

   from 
  those 
  of 
  the 
  seniculus 
  and 
  palliata, 
  groups. 
  

  

  Characters 
  of 
  hyoid 
  bones 
  of 
  the 
  various 
  species 
  of 
  howlers, 
  based 
  

   on 
  available 
  material, 
  and 
  figures 
  and 
  descriptions 
  of 
  hyoid 
  bones 
  

   supplied 
  by 
  Ihering 
  and 
  Lonnberg 
  are 
  summarized 
  as 
  follows: 
  

  

  1. 
  A. 
  seniculus 
  group. 
  

  

  a. 
  A. 
  seniculus 
  seniculus. 
  

  

  Male: 
  Hyoid 
  large, 
  tentorium 
  inflated 
  to 
  form 
  large 
  chamber 
  with 
  bony 
  

   lateral 
  partitions; 
  cornua 
  absent, 
  tentorium 
  with 
  well-marked 
  articular 
  

   depression 
  for 
  thyreohyal; 
  cornicula 
  reduced 
  or 
  obsolete; 
  rounded 
  

   mouth 
  of 
  bulla 
  relatively 
  small, 
  constricted 
  at 
  rim; 
  inner 
  surface 
  of 
  

   bulla 
  parted 
  by 
  at 
  least 
  a 
  midventral 
  line 
  or 
  bony 
  ridge. 
  

  

  Female: 
  As 
  described 
  in 
  text, 
  p. 
  394. 
  

  

  b. 
  A. 
  seniculus 
  slraminea. 
  

  

  Male: 
  As 
  in 
  seniculus 
  ("a" 
  above) 
  but 
  short 
  stalklike 
  cornua 
  with 
  

   rounded 
  articular 
  surfaces 
  present; 
  mouth 
  of 
  bulla 
  smaller, 
  its 
  trans- 
  

   verse 
  diameter 
  greater 
  than 
  sagittal 
  diameter. 
  

  

  Female: 
  As 
  in 
  female 
  seniculus 
  but 
  tentorium 
  less 
  inflated, 
  cornicula 
  well 
  

   developed, 
  long, 
  projecting, 
  and 
  tapering 
  to 
  a 
  point. 
  

  

  