﻿268 
  Mr. 
  R. 
  C. 
  L. 
  Perkins 
  on 
  

  

  Andreniform 
  habitus, 
  with 
  the 
  ordinary 
  triangular 
  pygidial 
  

   area. 
  

  

  As 
  to 
  Nomada 
  it 
  was 
  correctly 
  placed 
  by 
  the 
  old 
  Hymeno- 
  

   pterists 
  Kirby 
  and 
  Jurine 
  next 
  to 
  Epeolus, 
  and 
  is 
  Antho- 
  

   phorid, 
  not 
  in 
  the 
  least 
  allied 
  to 
  the 
  Megachilidae 
  as 
  Perez 
  

   concluded, 
  and 
  also 
  very 
  remote 
  from 
  existing 
  Andrenidae, 
  

   where 
  Edward 
  Saunders 
  finally 
  placed 
  it. 
  The 
  genital 
  

   armature 
  of 
  the 
  male 
  is 
  to 
  my 
  eyes 
  essentially 
  Antho- 
  

   phorid, 
  and 
  is 
  not 
  at 
  all 
  like 
  either 
  Megachile 
  or 
  Andrena, 
  

   and 
  the 
  form 
  of 
  labrum 
  is 
  conclusive, 
  not 
  to 
  mention 
  other 
  

   characters. 
  At 
  the 
  most 
  one 
  might 
  allow 
  that 
  its 
  ancestors 
  

   left 
  the 
  Panurgine 
  branch 
  of 
  Andrena 
  at 
  a 
  time 
  when 
  

   these 
  were 
  not 
  well 
  differentiated, 
  but 
  I 
  think 
  this 
  unlikely. 
  

  

  Of 
  great 
  interest 
  is 
  the 
  condition 
  of 
  the 
  $ 
  ventral 
  abdo- 
  

   minal 
  segments 
  in 
  the 
  three 
  parasitic 
  genera. 
  In 
  Meleda 
  

   the 
  6th 
  segment 
  is 
  extremely 
  narrow 
  and 
  compressed 
  ; 
  in 
  

   Epeohts 
  and 
  Nomada 
  it 
  is 
  capable 
  of 
  entire 
  retraction 
  

   beneath 
  the 
  5th 
  and 
  has 
  a 
  special 
  armature, 
  so 
  that 
  one 
  

   may 
  sometimes 
  count 
  only 
  5 
  ventral 
  segments. 
  In 
  all 
  

   our 
  Nomadas 
  it 
  is 
  armed 
  on 
  each 
  side 
  at 
  the 
  apex 
  with 
  

   some 
  close-set 
  strong 
  spines, 
  and 
  it 
  differs 
  in 
  thickness 
  in 
  

   different 
  parts. 
  In 
  Epeolus 
  it 
  is 
  produced 
  on 
  each 
  side 
  

   into 
  two 
  long 
  processes, 
  which 
  are 
  serrated 
  on 
  the 
  edge. 
  

   If 
  one 
  imagines 
  the 
  apical 
  and 
  median 
  thinner 
  portion 
  of 
  

   the 
  segment 
  in 
  Nomada 
  removed, 
  two 
  armed 
  processes 
  

   would 
  be 
  formed 
  in 
  this 
  genus 
  also. 
  

  

  Whilst 
  Nomada 
  still 
  remains 
  connected 
  with 
  the 
  Antho- 
  

   phoridae 
  by 
  the 
  parasitism 
  of 
  N. 
  sexfasciafa 
  on 
  the 
  An- 
  

   thophorid 
  Eucera, 
  Epeolus, 
  so 
  far 
  as 
  I 
  know, 
  has 
  become 
  

   parasitic 
  only 
  on 
  CoUetes, 
  which 
  is 
  almost 
  as 
  far 
  removed 
  

   from 
  the 
  Anthophoridae 
  in 
  one 
  direction 
  as 
  can 
  be 
  

   imagined. 
  

  

  CHARACTERS 
  OF 
  GROUPS 
  AND 
  SPECIES. 
  

  

  The 
  characters 
  given 
  in 
  the 
  tables 
  have 
  been 
  taken 
  not 
  

   from 
  selected 
  single 
  examples 
  of 
  each 
  sex 
  supposed 
  to 
  be 
  

   typical, 
  nor 
  yet 
  from 
  any 
  special 
  series 
  of 
  specimens, 
  but 
  

   are 
  those 
  which 
  in 
  a 
  period 
  of 
  study 
  extending 
  over 
  thirty 
  

   years, 
  during 
  which 
  great 
  numbers 
  of 
  individuals 
  have 
  

   been 
  examined, 
  I 
  have 
  found 
  most 
  constant. 
  Smith 
  and 
  

   Saunders, 
  on 
  the 
  other 
  hand, 
  based 
  their 
  descriptions 
  

   essentially 
  on 
  individual 
  specimens, 
  and 
  placed 
  special 
  

   labels 
  on 
  those 
  selected. 
  In 
  some 
  cases 
  this 
  method 
  seems 
  

   to 
  me 
  to 
  have 
  resulted 
  in 
  characters 
  being 
  considered 
  as 
  of 
  

  

  