﻿324 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  Mesopleurum. 
  (Fig. 
  2.) 
  The 
  flanks 
  are 
  obliquely 
  inclined. 
  Tlie 
  epi- 
  

   ^ternnm 
  is 
  divided 
  into 
  a 
  supra-episternite 
  and 
  an 
  infra-episternitej 
  the 
  

   latter 
  is 
  trai)ezoidal, 
  a 
  little 
  longer 
  than 
  broad, 
  with 
  a 
  broad 
  projection 
  

   extending, 
  round 
  in 
  front, 
  resting 
  upon 
  the 
  mesosternum. 
  The 
  supra- 
  

   episternite 
  is 
  sub-diamond-shaped, 
  the 
  lower 
  edge 
  triangular, 
  fitting 
  into 
  

   the 
  infra 
  episternite. 
  

  

  The 
  epimerum 
  is 
  divided 
  into 
  two 
  pieces; 
  the 
  infra-epimerite 
  is 
  nearly 
  

   as 
  broad 
  as 
  long; 
  the 
  sub-epimerite 
  is 
  long, 
  oblique, 
  irregular 
  in 
  form, 
  

   with 
  three 
  large 
  projections 
  from 
  the 
  surface. 
  

  

  Trochantine 
  broad 
  and 
  short. 
  Coxa 
  small 
  compared 
  with 
  the 
  troch- 
  

   antine, 
  being 
  about 
  one-third 
  as 
  large. 
  

  

  Metapleurum. 
  (Fig. 
  3.) 
  Exactly 
  repeats 
  the 
  structure 
  of 
  the 
  meso- 
  

   pleurum, 
  except 
  that 
  it 
  is 
  a 
  little 
  longer, 
  as 
  the 
  hind 
  wings 
  are 
  larger 
  

   than 
  the 
  anterior 
  pair. 
  Coxa 
  and 
  trochantine 
  the 
  same 
  as 
  in 
  the 
  meso- 
  

   thorgx. 
  

  

  Sternum, 
  

  

  Prosternum 
  (Pteronarcys 
  calif 
  ornica), 
  (Fig. 
  4.) 
  Eepresented 
  only 
  by 
  

   a 
  swollen 
  fold 
  in 
  front 
  of 
  the 
  insertions 
  of 
  the 
  legs, 
  and 
  by 
  a 
  gill-bearing 
  

   membranous 
  swelling 
  behind. 
  In 
  Acroneuria 
  abnormis 
  there 
  is 
  a 
  broad, 
  

   large, 
  scutellate 
  chitinous 
  piece. 
  

  

  Mesosternum 
  {Pt. 
  californica). 
  (Fig. 
  5.) 
  This 
  sternite 
  consists 
  of 
  two 
  

   portions, 
  (1) 
  a 
  raised, 
  rounded 
  sclerite 
  (prsesternite) 
  longer 
  than 
  broad, 
  

   and 
  situated 
  on 
  the 
  front 
  of 
  the 
  sternal 
  area, 
  between 
  the 
  two 
  anterior 
  

   gills 
  ; 
  (2) 
  behind 
  is 
  the 
  true 
  sternum, 
  which 
  is 
  a 
  very 
  broad, 
  trans- 
  

   versely-oblong 
  sclerite, 
  square 
  on 
  the 
  sides, 
  and 
  about 
  one-fourth 
  as 
  

   long 
  as 
  broad, 
  and 
  somewhat 
  curvilinear. 
  In 
  Acroneuria 
  ahnormis 
  the 
  

   mesosternum 
  is 
  divided 
  into 
  (1) 
  a 
  large 
  pr£esternite, 
  which 
  is 
  broad 
  and 
  

   triangular; 
  and 
  (2) 
  a 
  large 
  trapezoidal 
  sternite. 
  

  

  Metasternum. 
  (Fig. 
  6.) 
  The 
  same 
  as 
  in 
  the 
  mesothorax, 
  but 
  slightly 
  

   larger. 
  Behind 
  the 
  sternite, 
  on 
  both 
  meso- 
  and 
  metathorax, 
  are 
  in 
  each 
  

   segment 
  two 
  deep 
  fossse, 
  extending 
  probably 
  into 
  the 
  ento 
  thorax 
  ( 
  medi- 
  

   an 
  d 
  postfurca). 
  In 
  Acroneuria 
  the 
  metasternum 
  is 
  the 
  same 
  in 
  form 
  as 
  

   the 
  mesosternum, 
  but 
  the 
  prcesternite 
  is 
  shorter 
  and 
  broader. 
  

  

  THE 
  UROSOME 
  (ABDOMEN). 
  

  

  In 
  Pteronarcys 
  californica 
  (PL 
  XLIY, 
  figs. 
  7-9) 
  there 
  are 
  ten 
  abdominal 
  

   segments 
  (uromeres). 
  The 
  tergites 
  are 
  ten 
  in: 
  number, 
  the 
  first 
  broad 
  

   and 
  well 
  developed, 
  the 
  tenth 
  small 
  and 
  very 
  short, 
  with 
  a 
  median 
  tri- 
  

   angular 
  projection 
  (supraanal 
  plate) 
  ; 
  the 
  segment 
  is 
  entire 
  but 
  very 
  

   short 
  sternally. 
  There 
  are 
  no 
  pleurites, 
  except 
  nearly 
  obsolete 
  mem- 
  

   branous 
  folds 
  on 
  the 
  first 
  and 
  second 
  uromeres, 
  on 
  which 
  the 
  first 
  and 
  

   second 
  pair 
  of 
  spiracles 
  are 
  situated 
  ; 
  on 
  the 
  other 
  uromeres 
  the 
  remain- 
  

   ing 
  six 
  pair 
  are 
  situated 
  on 
  the 
  lower 
  edge 
  of 
  the 
  tergites. 
  From 
  the 
  

   hinder 
  edge 
  of 
  the 
  eighth 
  urosternite 
  two 
  short, 
  stout 
  spines 
  project 
  

  

  