﻿68 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID^E 
  : 
  

  

  Though 
  Notosceles 
  is 
  in 
  several 
  respects 
  intermediate 
  between 
  Notopoides 
  

   and 
  Raninoides, 
  the 
  last-named 
  genus 
  (figs. 
  5 
  & 
  6) 
  has 
  many 
  distinctive 
  

   features, 
  most 
  of 
  which 
  may 
  be 
  explained 
  as 
  adaptations 
  to 
  a 
  swimming 
  

   habit. 
  The 
  carapace 
  is 
  elongated, 
  and 
  its 
  flanks 
  taper 
  so 
  evenly 
  posteriorly 
  

   that 
  it 
  may 
  fairly 
  be 
  described 
  as 
  boat-shaped. 
  The 
  first 
  abdominal 
  tergum 
  

   is 
  notably 
  narrower 
  than 
  the 
  posterior 
  margin 
  of 
  the 
  carapace, 
  and 
  the 
  whole 
  

   abdomen 
  is 
  narrow 
  and 
  more 
  distinctly 
  flexed 
  under 
  the 
  thorax 
  than 
  is 
  usual 
  

   in 
  Baninidse. 
  On 
  the 
  ventral 
  surface 
  there 
  is 
  a 
  broad 
  and 
  long 
  flat 
  plastron 
  

   in 
  the 
  formation 
  of 
  which 
  the 
  eleventh 
  and 
  twelfth 
  sterna 
  take 
  an 
  even 
  larger 
  

   share 
  than 
  the 
  tenth 
  (fig. 
  6). 
  The 
  twelfth 
  sternum 
  is 
  of 
  considerable 
  length 
  

   antero-posteriorly 
  and 
  is 
  also 
  broad 
  and 
  nearly 
  flat. 
  The 
  articular 
  cavities 
  

   of 
  the 
  second 
  pair 
  of 
  pereiopods 
  are 
  placed 
  at 
  its 
  hinder 
  border 
  and 
  face 
  

   backwards. 
  The 
  thirteenth 
  sternum 
  being 
  very 
  short, 
  the 
  articular 
  cavities 
  

   of 
  the 
  third 
  pereiopods 
  are 
  close 
  to 
  those 
  of 
  the 
  second, 
  and 
  the 
  two 
  pairs 
  of 
  

   limbs, 
  whilst 
  closely 
  contiguous 
  to 
  one 
  another, 
  are 
  separated 
  by 
  the 
  whole 
  

   length 
  of 
  the 
  twelfth 
  sternum 
  from 
  the 
  first 
  pereiopods. 
  The 
  last 
  pair 
  of 
  

   pereiopods 
  are 
  so 
  reduced 
  and 
  slender 
  that 
  they 
  are 
  usually 
  described 
  as 
  fili- 
  

   form 
  ; 
  they 
  terminate 
  in 
  minute 
  pointed 
  dactyli. 
  The 
  reduction 
  of 
  the 
  last 
  

   pair 
  of 
  legs 
  and 
  the 
  narrowing 
  of 
  the 
  base 
  of 
  the 
  abdomen 
  seems 
  to 
  be 
  cor- 
  

   related 
  with 
  the 
  suppression 
  of 
  the 
  posterior 
  branchial 
  orifices 
  ; 
  at 
  any 
  rate, 
  

   I 
  can 
  find 
  no 
  trace 
  of 
  these 
  orifices 
  in 
  Raninoides. 
  Nor 
  could 
  they 
  be 
  of 
  

   much 
  service 
  if 
  present, 
  for 
  the 
  external 
  water 
  conduits 
  which 
  in 
  other 
  

   forms 
  admit 
  of 
  a 
  flow 
  of 
  filtered 
  water 
  to 
  these 
  orifices 
  are 
  here 
  wanting. 
  

   Though 
  the 
  eleventh, 
  twelfth, 
  and 
  thirteenth 
  thoracic 
  epimera 
  are 
  as 
  much 
  

   exposed 
  to 
  the 
  surface 
  in 
  Raninoides 
  as 
  in 
  other 
  Raninidoe, 
  they 
  are 
  not 
  con- 
  

   cave 
  and 
  are 
  scarcely 
  overhung 
  by 
  the 
  edge 
  of 
  the 
  branchiostegite. 
  The 
  

   epimeron 
  of 
  the 
  eleventh 
  somite 
  is 
  relatively 
  small, 
  and 
  so 
  far 
  from 
  being- 
  

   concave 
  that 
  it 
  is 
  slightly 
  convex. 
  The 
  epimera 
  of 
  the 
  twelfth 
  and 
  thirteenth 
  

   somites 
  are 
  obliquely 
  grooved, 
  and 
  into 
  these 
  grooves 
  the 
  meri 
  of 
  the 
  second 
  

   and 
  third 
  pereiopods, 
  when 
  bent 
  forwards 
  and 
  pressed 
  against 
  the 
  sides 
  

   of 
  the 
  body, 
  fit 
  so 
  closely 
  that 
  no 
  water 
  can 
  pass 
  between, 
  The 
  first 
  

   pair 
  of 
  pereiopods 
  are 
  slender, 
  and 
  when 
  at 
  rest 
  are 
  directed 
  forwards, 
  

   their 
  large 
  cordate 
  dactyli 
  being 
  pressed 
  against 
  the 
  bases 
  of 
  the 
  cheli- 
  

   peds. 
  Their 
  function 
  is 
  obscure, 
  but 
  probably 
  they 
  are 
  used 
  for 
  digging. 
  

   The 
  characters 
  of 
  the 
  second 
  and 
  third 
  pereiopods 
  are 
  clearly 
  shown 
  in 
  

   fig. 
  6. 
  In 
  these 
  limbs 
  the 
  coxa 
  and 
  basis 
  are 
  directed 
  backwards 
  : 
  the 
  short 
  

   ischium 
  is 
  nearly 
  transverse 
  to 
  the 
  long 
  axis 
  of 
  the 
  body 
  : 
  the 
  merus 
  is 
  long 
  

   and 
  slender 
  : 
  the 
  carpus 
  normal, 
  but 
  it 
  is 
  to 
  be 
  observed 
  that 
  both 
  it 
  and 
  the 
  

   merus 
  are 
  scantily 
  furnished 
  with 
  short 
  hairs. 
  The 
  propodus 
  and 
  dactylus 
  

   are 
  flat 
  and 
  greatly 
  expanded 
  and 
  the 
  " 
  fan-hinge 
  " 
  between 
  them 
  

   is 
  a 
  noticeable 
  feature. 
  A 
  fringe 
  of 
  long 
  stiff 
  hairs 
  is 
  borne 
  on 
  the 
  

   hind 
  edge 
  of 
  the 
  propodus 
  and 
  on 
  the 
  inner 
  margin 
  of 
  the 
  dactylus. 
  The 
  

  

  