﻿16 
  Mr. 
  R. 
  I. 
  Pocock 
  on 
  the 
  

  

  externally 
  with 
  a 
  short 
  process 
  which 
  terminates 
  in 
  a 
  sharp 
  

   point. 
  

  

  Telson 
  much 
  shorter 
  than 
  lateral 
  portions 
  of 
  tail-fin 
  ; 
  lateral 
  

   margins 
  converging 
  ; 
  posterior 
  margin 
  slightly 
  convex, 
  fur- 
  

   nished 
  with 
  a 
  fringe 
  of 
  hairs 
  and 
  three 
  spines, 
  two 
  lateral 
  

   and 
  one 
  median, 
  and 
  often 
  some 
  smaller 
  minute 
  spines. 
  

   Upper 
  surface 
  behind 
  longitudinally 
  scooped 
  out 
  on 
  each 
  

   side 
  of 
  the 
  middle 
  line, 
  leaving 
  a 
  carina 
  between. 
  The 
  ex- 
  

   ternal 
  margins 
  of 
  the 
  grooves 
  are 
  adorned 
  with 
  a 
  curved 
  series 
  

   of 
  six 
  or 
  seven 
  spines. 
  

  

  Measurement 
  in 
  millimetres 
  of 
  largest 
  specimen. 
  — 
  Total 
  

   length 
  (from 
  apex 
  of 
  rostrum 
  to 
  end 
  of 
  telson) 
  117, 
  of 
  cara- 
  

   pace 
  (from 
  orbit 
  to 
  posterior 
  margin) 
  41 
  ; 
  width 
  of 
  carapace 
  

   24, 
  height 
  27 
  ; 
  length 
  of 
  rostrum 
  (from 
  hinder 
  edge 
  of 
  orbit 
  

   to 
  apex) 
  8£, 
  width 
  5 
  ; 
  length 
  of 
  antennular 
  peduncle 
  15, 
  of 
  

   antennal 
  scale 
  18, 
  of 
  peduncle 
  15 
  ; 
  1st 
  pereiopod 
  : 
  length 
  of 
  

   ischio-merus 
  15, 
  carpus 
  4, 
  propodus 
  and 
  dactylus 
  11 
  ; 
  3rd, 
  

   4th, 
  and 
  5th 
  pereiopoda 
  (measured 
  along 
  external 
  margin) 
  : 
  

   merus 
  34, 
  26, 
  17, 
  carpus 
  13^, 
  11, 
  10£, 
  propodus 
  16, 
  15, 
  17 
  ; 
  

   length 
  of 
  telson 
  15, 
  of 
  exopodite 
  of 
  tail-fin 
  20, 
  endopodite 
  18. 
  

  

  Atya 
  scabra 
  (Leach) 
  is 
  the 
  only 
  American 
  species 
  with 
  

   which, 
  owing 
  to 
  my 
  having 
  seen 
  specimens 
  of 
  it, 
  I 
  can 
  com- 
  

   pare 
  occidentalis. 
  In 
  scabra, 
  apart 
  from 
  other 
  less 
  noticeable 
  

   differences, 
  the 
  third 
  pereiopods 
  are 
  stouter, 
  more 
  sparsely 
  

   tuberculated, 
  and 
  the 
  ischio-merus 
  is 
  more 
  sharply 
  angulated 
  

   above 
  and 
  entirely 
  smooth 
  on 
  the 
  inner 
  surface. 
  

  

  The 
  following 
  species 
  I 
  know 
  only 
  from 
  descriptions 
  : 
  — 
  

  

  Atya 
  rivalis, 
  S. 
  I. 
  Smith, 
  Rep. 
  Peabody 
  Acad. 
  Sci. 
  1871, 
  

  

  p. 
  94. 
  — 
  Nicaragua. 
  

  

  tenella, 
  id. 
  ibid 
  — 
  Nicaragua. 
  

  

  punctata, 
  J. 
  S. 
  Kingsley, 
  Proc. 
  Acad. 
  Nat. 
  Sci. 
  Phil. 
  

  

  1878, 
  p. 
  94.— 
  Hayti. 
  

  

  But 
  the 
  features 
  pointed 
  out 
  by 
  Mr. 
  Kingsley 
  to 
  distinguish 
  

   his 
  punctata 
  from 
  occidentalis, 
  rivalis, 
  and 
  tenella, 
  not 
  to 
  

   mention 
  scabra, 
  are 
  merely 
  such 
  as 
  in 
  the 
  present 
  paper 
  have 
  

   been 
  regarded 
  as 
  due 
  either 
  to 
  individual 
  variation 
  or 
  to 
  differ- 
  

   ence 
  of 
  age. 
  

  

  ? 
  Caridina 
  americana, 
  Gue*rin. 
  

  

  Caridina 
  americana, 
  Guenn, 
  Ramon 
  de 
  la 
  Sagra, 
  Cuba 
  Crust, 
  p. 
  52, 
  

   pi. 
  ii. 
  fig. 
  13 
  ; 
  von 
  Martens, 
  Arch. 
  f. 
  Naturg. 
  1872, 
  p. 
  135. 
  

  

  Two 
  females, 
  with 
  ova, 
  taken 
  at 
  Laiou. 
  

  

  