﻿36 
  DR. 
  G. 
  C. 
  BOUUNE 
  ON 
  THE 
  UANINID.E 
  : 
  

  

  edges 
  stop 
  some 
  way 
  short 
  o£ 
  the 
  middle 
  line 
  and 
  are 
  not 
  piolonged 
  into 
  

   conspicuous 
  endosternites. 
  Towards 
  their 
  lower 
  ends 
  they 
  do, 
  indeed, 
  give 
  

   off 
  triangular 
  or 
  thorn-shaped 
  offsets 
  (such 
  an 
  offset 
  is 
  shown 
  in 
  the 
  inter- 
  

   segmental 
  arthrophragm 
  x/xi 
  in 
  PI. 
  4. 
  fig. 
  12), 
  but 
  these 
  are 
  not 
  expanded 
  

   into 
  flattened 
  summits 
  and 
  do 
  not 
  come 
  into 
  contact 
  with 
  their 
  fellows 
  of 
  the 
  

   opposite 
  side 
  of 
  the 
  body. 
  Therefore 
  there 
  is 
  no 
  sternal 
  canal. 
  The 
  

   epimeral 
  apodemes 
  or 
  endopleurites 
  are 
  well-developed 
  in 
  crabs 
  and, 
  as 
  in 
  

   Macrura, 
  they 
  bifurcate 
  at 
  their 
  inner 
  ends, 
  the 
  anterior 
  bifurcation 
  uniting 
  

   with 
  the 
  intersegmental 
  apodeme 
  in 
  front, 
  the 
  posterior 
  bifurcation 
  with 
  the 
  

   intersegmental 
  apodeme 
  next 
  behind, 
  as 
  is 
  shown 
  in 
  fig. 
  12. 
  It 
  should 
  be 
  

   noted 
  that 
  in 
  all 
  these 
  respects 
  Dromia 
  has 
  departed 
  so 
  far 
  from 
  itsMacruran 
  

   ancestry 
  and 
  has 
  taken 
  on 
  so 
  completely 
  the 
  characters 
  of 
  crabs, 
  that 
  it 
  has 
  

   been 
  possible 
  to 
  make 
  use 
  of 
  it 
  as 
  a 
  typical 
  example 
  of 
  this 
  aspect 
  of 
  cancroid 
  

   structure. 
  

  

  If 
  we 
  now 
  bring 
  the 
  Raninidaa 
  into 
  comparison, 
  taking 
  as 
  our 
  example 
  

   Ranina 
  dentata, 
  we 
  find 
  a 
  curious 
  admixture 
  of 
  crab-like 
  and 
  Macruran 
  

   characters, 
  but 
  the 
  latter 
  predominate 
  and 
  the 
  former 
  must 
  be 
  called 
  1 
  

   deceptively 
  crab-like, 
  for 
  a 
  detailed 
  examination 
  shows 
  that 
  they 
  must 
  have 
  

   originated 
  independently, 
  in 
  relation 
  to 
  the 
  habits 
  of 
  the 
  animal, 
  and 
  not 
  by 
  

   way 
  of 
  inheritance 
  from 
  any 
  other 
  recognized 
  crabs. 
  

  

  In 
  the 
  first 
  place, 
  as 
  may 
  be 
  seen 
  by 
  a 
  comparison 
  of 
  PI. 
  5. 
  fig-. 
  13, 
  11, 
  and 
  

   15, 
  the 
  contour 
  of 
  the 
  thorax 
  of 
  Ranina 
  as 
  seen 
  from 
  behind 
  is 
  more 
  like 
  

   that 
  of 
  a 
  lobster 
  than 
  like 
  that 
  of 
  a 
  crab. 
  In 
  the 
  crab 
  the 
  width 
  of 
  the 
  

   thorax 
  largely 
  exceeds 
  its 
  height 
  ; 
  in 
  the 
  lobster 
  the 
  height 
  clearly 
  exceeds 
  

   the 
  width 
  ; 
  in 
  Ranina 
  the 
  height 
  is 
  rather 
  greater 
  than 
  the 
  width. 
  Looking 
  

   at 
  the 
  sternal 
  surface, 
  Ranina 
  has 
  a 
  broad 
  ventral 
  plastron 
  and 
  in 
  so 
  far 
  

   resembles 
  a 
  crab, 
  but 
  the 
  most 
  cursory 
  inspection 
  shows 
  that 
  it 
  is 
  made 
  up 
  

   almost 
  entirely 
  of 
  the 
  greatly 
  enlarged 
  and 
  flattened 
  sternum 
  of 
  the 
  tenth 
  

   segment. 
  The 
  more 
  posterior 
  thoracic 
  sterna, 
  particularly 
  those 
  of 
  the 
  

   twelfth 
  and 
  thirteenth 
  segments, 
  are 
  narrow 
  and 
  keel-like 
  ; 
  indeed, 
  they 
  are 
  

   proportionately 
  narrower 
  than 
  in 
  the 
  lobster. 
  The 
  broad 
  sternum 
  of 
  the 
  

   tenth 
  segment 
  is 
  fiat 
  and 
  has 
  no 
  vertical 
  depth 
  ; 
  that 
  of 
  the 
  eleventh 
  

   segment 
  has 
  the 
  form 
  of 
  a 
  pair 
  of 
  aliform 
  expansions 
  extending 
  along 
  the- 
  

   posterior 
  edges 
  of 
  the 
  twelfth 
  sternum 
  and 
  making 
  up 
  with 
  it 
  the 
  ventral 
  

   plastron. 
  Posteriorly 
  these 
  aliform 
  sclerites 
  meet 
  in 
  the 
  middle 
  line 
  to 
  form 
  

   the 
  short 
  and 
  somewhat 
  thickened 
  body 
  of 
  the 
  eleventh 
  sternum, 
  tilted 
  

   somewhat 
  upward. 
  The 
  twelfth 
  sternum 
  is 
  very 
  narrow, 
  of 
  considerable 
  

   vertical 
  depth, 
  and 
  is 
  curved 
  upwards. 
  The 
  thirteenth 
  and 
  fourteenth 
  sterna 
  

   are 
  still 
  deeper 
  vertically, 
  and 
  are 
  so 
  much 
  tilted 
  upwards 
  that 
  the 
  cavities 
  of 
  

   the 
  third 
  pair 
  of 
  pereiopods 
  look 
  nearl} 
  r 
  directly 
  backwards 
  and 
  the 
  cavities 
  

   of 
  the 
  fourth 
  pair 
  look 
  backwards 
  and 
  upwards 
  (PI. 
  5. 
  fig. 
  11). 
  The 
  large 
  

   articular 
  cavities 
  of 
  the 
  chelipeds 
  are 
  placed 
  laterally, 
  but 
  those 
  of 
  the 
  first 
  

  

  