﻿Palceozoic 
  Bivalved 
  Entomostraca. 
  

  

  385 
  

  

  February 
  1856, 
  pi. 
  vii. 
  fig. 
  16) 
  and 
  P. 
  muta 
  {op. 
  cit. 
  ser. 
  3, 
  

   vol. 
  ii. 
  1858, 
  pi. 
  ix. 
  fig. 
  3) 
  were 
  added 
  to 
  the 
  group 
  because 
  

   of 
  the 
  existence 
  of 
  such 
  passage-forms 
  (with 
  obsolete 
  sulci) 
  as 
  

   P. 
  Beyrichiana 
  and 
  pusilla, 
  J. 
  & 
  H., 
  connecting 
  them 
  with 
  

   the 
  true 
  Pvimitue. 
  To 
  these 
  non-sulcate 
  forms 
  may 
  be 
  added 
  

   P. 
  lenticularis, 
  J. 
  & 
  H., 
  1869, 
  P. 
  Sanctojohannesiana, 
  

   Lloydiana, 
  and 
  Milneana, 
  Jones, 
  Ann. 
  & 
  Mag. 
  Nat. 
  Hist. 
  

   November 
  1881, 
  pi. 
  xx. 
  figs. 
  1-3 
  ; 
  and 
  to 
  the 
  passage-forms, 
  

   var. 
  breviata 
  of 
  the 
  sulcate 
  P. 
  valida, 
  J. 
  & 
  H., 
  1886: 
  P. 
  

   cylindrica 
  (Holl) 
  and 
  P. 
  minuta 
  (Eichwald) 
  possibly 
  also 
  

   belong 
  to 
  this 
  non-sulcate 
  group. 
  

  

  Fig. 
  10 
  and 
  woodcuts, 
  figs. 
  5 
  and 
  6 
  (specimen 
  no. 
  2 
  of 
  the 
  

   whole 
  series), 
  illustrate 
  a 
  subglobular 
  Leperditioid 
  Ostracod 
  

   with 
  strong 
  dorsal 
  angles 
  fore 
  and 
  aft, 
  and 
  a 
  steep 
  postero- 
  

   dorsal 
  and 
  more 
  gentle 
  antero-dorsal 
  slope, 
  the 
  former 
  falling 
  

   into 
  a 
  bolder 
  curve 
  than 
  the 
  latter; 
  and 
  with 
  the 
  ventral 
  outline 
  

   almost 
  semicircular. 
  The 
  ventral 
  and 
  end 
  margins 
  of 
  the 
  

   united 
  valves 
  are 
  thick 
  and 
  bevelled 
  inwards 
  and 
  slightly 
  

   fluted 
  there 
  (see 
  woodcuts, 
  figs. 
  5 
  and 
  6). 
  This 
  character 
  

   approaches 
  that 
  shown 
  by 
  fig. 
  1 
  c 
  in 
  pi. 
  vii., 
  Ann. 
  & 
  Mag. 
  

   Nat. 
  Hist. 
  July 
  1868, 
  in 
  a 
  much 
  less 
  Leperditioid 
  carapace, 
  

   which 
  we 
  referred 
  to 
  the 
  smooth 
  or 
  non-sulcate 
  Primitive 
  (P. 
  

   Maccoi/ii, 
  J. 
  & 
  H.). 
  As 
  it 
  has 
  not 
  been 
  figured 
  for 
  Iso- 
  

   chilina, 
  and 
  is 
  very 
  distinct 
  from 
  the 
  ventral 
  edge 
  of 
  Leper- 
  

   ditia, 
  it 
  may 
  still 
  be 
  regarded 
  as 
  characteristic 
  of 
  the 
  non- 
  

   sulcate 
  Primitian 
  group 
  here 
  indicated, 
  and 
  which 
  I 
  take 
  

   this 
  opportunity 
  of 
  defining 
  as 
  a 
  generic 
  group 
  separable 
  from 
  

   Primitia 
  (though 
  there 
  are 
  some 
  passage-forms) 
  as 
  Apar- 
  

   CHITES. 
  

  

  Fie:. 
  5. 
  

  

  Fur. 
  0. 
  

  

  Figs. 
  5 
  and 
  G. 
  — 
  Aparchites 
  WMteavesii, 
  now, 
  magnified 
  10 
  diameters. 
  

  

  5. 
  Front 
  end 
  view. 
  6. 
  Ventral 
  view. 
  

  

  [See 
  Plate 
  XVII. 
  fig- 
  10.] 
  

  

  In 
  its 
  outline 
  the 
  individual 
  under 
  notice, 
  from 
  Manitoba, 
  

   is 
  shorter 
  and 
  rounder 
  than 
  Leperditia 
  rotundata, 
  Walcott 
  

   (Pakuont. 
  Eureka 
  &c, 
  1884, 
  p. 
  206, 
  pi. 
  xvi. 
  fig. 
  5), 
  and 
  in 
  

  

  