357 
Length  about  58  mm.;  width  of  10th  somite  6.5;  of  l»t  5.5,  length 
of  1st  2.3. 
52.  Platyrhachus  œquidens  sp.  n.  Pl.  XXI,  fig.  3  — 3b. 
Sumatra:  Ajer  Mantjur. 
So  closely  related  to  the  preceding  species  as  to  render  a  detailed 
description  unnecessary. 
Colour;  head,  antennas  fuscous;  somites  nearly  black,  the  keels 
being  yellowish  white ,  with  the  black  of  the  dorsal  surface  spreading 
on  to  them  at  the  base;  lower  surface  and  legs  paler. 
The  keels  have  very  much  the  same  form,  being  strongly  bidentate 
owing  to  the  deep  mesial  emargination  of  the  lateral  border.  The 
two  teeth  however  are  stouter,  being  less  cylindrical  and  more  trian- 
gular, and  the  keels  themselves  are  less  elevated,  giving  the  back  a 
flatter  aspect. 
Copulatory  foot  very  much  like  that  of  the,  preceding,  but  the 
upper  terminal  process  is  more  abruptly  curved  backwards,  and  the 
lower  one  less  so. 
Length  about  52  mm.;  width  of  10th  somite  6;  of  lst  4.5,  length 
of  1st  2. 
Two  male  examples. 
53.  Platyrhachus  inœquidens,  sp.  n.  Pl.  XXII,  fig.  1  —  1  a. 
Sumatra:  Manindjau. 
Related  to  both  the  preceding  species. 
Colour  ferrugino-piceous,  external  half  of  the  keels  flavous;  sternal 
surfaces  and  legs  ochraceous. 
Keels  of  the  first  segment  smaller,  horizontal,  taking  the  form  of 
a  pointed  tubercle  on  each  side.  Those  of  the  second,  third  and  fourth 
wider  than  they  are  long,  projecting  lightly  upwards  and  becoming 
gradually  more  conspicuously  bidentate  from  before  backwards.  The 
rest  of  the  keels  longer  than  wide,  directed  slightly  backwards  and 
slightly  upwards,  the  anterior  border  directed  more  strongly  back- 
wards than  the  posterior  border,  with  a  distinct  shoulder  at  its  base, 
the  lateral  border  deeply  but  irregularly  excised  and  consequently 
bidentate,  the  two  teeth  generaly  bifid  at  the  apex,  subequal  in  size 
in  the  anterior  half  of  the  body,  but  the  anterior  decreases  in  size 
and  becomes  almost  spiniform  in  the  posterior  half.  The  pores  situated 
