﻿[33] 
  ANNELIDA 
  CH^TOPODA. 
  739 
  

  

  a 
  stout 
  fleshy 
  plate, 
  from 
  the 
  middle 
  of 
  the 
  concave 
  outer 
  margin 
  of 
  

   which 
  arises 
  a 
  stout 
  conical 
  cirrus. 
  The 
  dorsal 
  aud 
  veutral 
  rami 
  are 
  

   distinct 
  and 
  remote 
  from 
  each 
  other 
  on 
  the 
  first 
  twelve 
  segments, 
  but 
  

   behind 
  this 
  segment 
  they 
  both 
  arise 
  from 
  a 
  low, 
  rounded, 
  fleshy 
  lip, 
  

   having 
  a 
  shallow 
  depression 
  between 
  the 
  rami. 
  This 
  plate 
  is 
  continued 
  

   to 
  the 
  base 
  of 
  the 
  branchiae, 
  and 
  crosses 
  the 
  dorsum 
  as 
  a 
  low, 
  rounded 
  

   ridge. 
  Below 
  the 
  ventral 
  ramus 
  it 
  widens, 
  and 
  forms 
  low, 
  rounded 
  

   lobes, 
  so 
  wide 
  near 
  the 
  ramus 
  that 
  they 
  are 
  separated 
  from 
  each 
  other 
  

   only 
  by 
  the 
  lines 
  of 
  segmentation; 
  passing 
  downward 
  they 
  become 
  

   narrower. 
  

  

  Each 
  segment 
  is 
  distinctly 
  triauulate. 
  The 
  anal 
  segment 
  ends 
  in 
  four 
  

   flattened 
  lobes, 
  bluntly 
  rounded 
  behind 
  — 
  one 
  dorsal, 
  one 
  ventral, 
  two 
  

   lateral 
  ; 
  from 
  each 
  of 
  these 
  lobes 
  arises 
  an 
  anal 
  cirrus, 
  rather 
  stout, 
  

   slightly 
  tapering, 
  as 
  long 
  as 
  the 
  last 
  five 
  segments. 
  

  

  Common 
  at 
  half- 
  tide, 
  under 
  stones 
  ; 
  gregarious. 
  

  

  ARICIDEA 
  Webster. 
  

   Aricidea 
  quadeilobata 
  n. 
  sp. 
  

  

  (Pl. 
  VII, 
  Figs. 
  93-96.) 
  

  

  Iu 
  this 
  species 
  the 
  head 
  (fig. 
  93) 
  is 
  constricted 
  a 
  little 
  behind 
  the 
  

   middle, 
  broadly 
  rounded 
  in 
  front 
  ; 
  posterior 
  part 
  convex; 
  anterior 
  part 
  

   sloping, 
  so 
  as 
  to 
  be 
  much 
  thinner 
  in 
  front 
  than 
  behind. 
  

  

  The 
  antenna 
  is 
  delicate, 
  almost 
  filiform, 
  reaching 
  back 
  to 
  the 
  sixth 
  

   setigerous 
  segment. 
  A 
  pair 
  of 
  minute 
  red 
  eyes, 
  about 
  half 
  way 
  between 
  

   the 
  origin 
  of 
  the 
  antenna 
  and 
  the 
  sides 
  of 
  the 
  head. 
  

  

  The 
  buccal 
  segment 
  is 
  short, 
  without 
  rami; 
  it 
  carries 
  four 
  oval 
  eleva- 
  

   tions, 
  arranged 
  in 
  a 
  series, 
  about 
  equally 
  distant 
  from 
  each 
  other. 
  

  

  The 
  next 
  three 
  segments 
  carry 
  both 
  dorsal 
  and 
  ventral 
  cirri, 
  conical 
  

   and 
  slightly 
  fusiform, 
  the 
  ventral 
  somewhat 
  larger 
  than 
  the 
  dorsal. 
  

  

  The 
  brauchiaB 
  begin 
  on 
  the 
  fourth 
  setigerous 
  segment 
  ; 
  there 
  are 
  nine 
  

   pairs. 
  They 
  are 
  broad 
  at 
  base 
  (fig. 
  94), 
  do 
  not 
  taper 
  much 
  along 
  their 
  

   inner 
  two-thirds, 
  then 
  suddenly 
  become 
  pointed. 
  They 
  are 
  usually 
  ap- 
  

   plied 
  closely 
  to 
  the 
  body, 
  aud 
  would 
  overlap, 
  but 
  the 
  pointed 
  ends 
  turn 
  

   suddenly 
  backward. 
  

  

  The 
  dorsal 
  cirri, 
  on 
  the 
  branchiated 
  segments, 
  are 
  more 
  delicate 
  than 
  

   on 
  the 
  anterior 
  segments, 
  and 
  slightly 
  swollen 
  externally, 
  near 
  their 
  

   origin 
  ; 
  back 
  of 
  the 
  branchiated 
  segments 
  these 
  cirri 
  become 
  very 
  deli- 
  

   cate, 
  filiform 
  (figs. 
  95, 
  96), 
  and, 
  on 
  the 
  posterior 
  segments, 
  their 
  length 
  

   surpasses 
  the 
  width 
  of 
  the 
  body. 
  

  

  The 
  dorsal 
  setae 
  are 
  all 
  simple, 
  capillary 
  ; 
  they 
  increase 
  in 
  length 
  

   with 
  the 
  dorsal 
  cirri, 
  so 
  that 
  even 
  on 
  the 
  posterior 
  segments 
  some 
  of 
  

   these 
  setae 
  project 
  beyond 
  the 
  cirri. 
  The 
  ventral 
  setae 
  are 
  shorter 
  than 
  

   the 
  dorsal; 
  arranged 
  in 
  a 
  close-set 
  fan 
  ; 
  on 
  the 
  posterior 
  segments 
  a 
  few 
  

   of 
  these 
  setae 
  have 
  a 
  sigmoid 
  flexure 
  near 
  the 
  end. 
  

  

  