﻿STRUCTURE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  ARACHNJDA. 
  229 
  

  

  ( 
  = 
  opistliosoma) 
  not 
  more 
  than 
  ten 
  in 
  nnmber, 
  distinct 
  or 
  

   coalesced. 
  

  

  Family 
  — 
  Limnlidai 
  (L 
  i 
  m 
  nl 
  ii 
  s) 
  . 
  

  

  ,, 
  Belinurid^ 
  (BelinuruSj 
  A 
  gl 
  as 
  pis, 
  Prest- 
  

  

  w 
  i 
  c 
  li 
  i 
  a) 
  . 
  

   „ 
  Hemiaspidas 
  (Hemiaspis, 
  Bunodes). 
  

  

  Remarks. 
  — 
  The 
  Xiphosura 
  are 
  marine 
  in 
  habit^ 
  frequenting* 
  

   the 
  shore. 
  They 
  are 
  represented 
  at 
  the 
  present 
  day 
  by 
  the 
  

   single 
  genus 
  Limulus 
  (Figs. 
  44 
  and 
  45; 
  also 
  Figs. 
  1, 
  9_, 
  11, 
  to 
  

   15 
  and 
  20), 
  wliich 
  occurs 
  on 
  the 
  America 
  coast 
  of 
  the 
  Atlantic 
  

   Ocean, 
  but 
  not 
  on 
  its 
  eastern 
  coasts, 
  and 
  on 
  the 
  Asiatic 
  coast 
  

   of 
  the 
  Pacific. 
  The 
  Atlantic 
  species 
  (L. 
  polyphemus) 
  is 
  

   common 
  on 
  the 
  coasts 
  of 
  the 
  United 
  States, 
  and 
  is 
  known 
  as 
  

   the 
  king-crab 
  or 
  horseshoe 
  crab. 
  A 
  single 
  specimen 
  was 
  

   found 
  in 
  the 
  harbour 
  of 
  Copenhagen 
  in 
  the 
  eighteenth 
  century, 
  

   having 
  presumably 
  been 
  carried 
  over 
  by 
  a 
  ship 
  to 
  which 
  it 
  

   cluDg. 
  

  

  A 
  species 
  of 
  Limulus 
  is 
  found 
  in 
  the 
  Buntersandstein 
  of 
  

   the 
  Vosges; 
  L. 
  Walchi 
  is 
  abundant 
  in 
  the 
  Oolitic 
  lithographic 
  

   slates 
  of 
  Bavaria. 
  

  

  The 
  genera 
  Beliuurus, 
  Aglaspis, 
  Prestwichia, 
  Hemiaspis, 
  

   and 
  Bunodes 
  consist 
  of 
  small 
  forms 
  which 
  occur 
  in 
  Palasozoic 
  

   rocks. 
  In 
  none 
  of 
  them 
  are 
  the 
  appendages 
  known, 
  but 
  in 
  

   the 
  form 
  of 
  the 
  two 
  carapaces 
  and 
  the 
  presence 
  of 
  free 
  

   somites 
  they 
  are 
  distinctly 
  intermediate 
  between 
  Limulus 
  and 
  

   the 
  Trilobitge. 
  The 
  young 
  form 
  of 
  Limulus 
  itself 
  (Fig. 
  40) 
  is 
  

   also 
  similar 
  to 
  a 
  Trilobite 
  so 
  far 
  as 
  its 
  segmentation 
  and 
  

   trilobation 
  are 
  concerned. 
  The 
  lateral 
  eyes 
  of 
  Limulus 
  

   appear 
  to 
  be 
  identical 
  in 
  structure 
  and 
  position 
  with 
  those 
  of 
  

   certain 
  Trilobitse. 
  

  

  Order 
  2. 
  Gigantostraca 
  (Figs. 
  46, 
  47). 
  — 
  Free-swimmingforms, 
  

   with 
  the 
  appendages 
  of 
  the 
  sixth 
  or 
  fifth 
  and 
  sixth 
  pairs 
  

   flattened 
  or 
  lengthened 
  to 
  act 
  as 
  oars 
  ; 
  segments 
  of 
  meso- 
  

   soma 
  and 
  metasoma 
  (= 
  opisthosoma) 
  twelve 
  in 
  number. 
  

   Appendages 
  of 
  anterior 
  pair 
  very 
  large 
  and 
  chelate. 
  

  

  Sub-order 
  Pterygotomorpha, 
  Pterygotidae 
  (Ptery- 
  

   gotus). 
  

  

  VOL. 
  48, 
  PART 
  2. 
  NEW 
  SEKIES. 
  16 
  

  

  