﻿860 
  PEOCEEDINGS 
  OF 
  THE 
  XATIOXJL 
  MUSEUM. 
  vol.xx. 
  

  

  MICROYOLDIA 
  Verrill 
  and 
  Bush, 
  1897. 
  

   Mieroijoldia 
  Vehkill 
  and 
  BusH, 
  Amer. 
  Joiun. 
  Sci., 
  Ill, 
  i)p. 
  5(5, 
  62, 
  Jaimary, 
  1897. 
  

  

  Type. 
  — 
  Mieroijoldia 
  regularis 
  (Yerrill). 
  

  

  Shell 
  small, 
  tiglitly 
  closed, 
  veueriform, 
  with 
  the 
  anterior 
  end 
  shortest 
  

   and 
  with 
  the 
  beaks 
  turned 
  forward. 
  A 
  ijosterior 
  marginal 
  ligament 
  in 
  

   a 
  distinct 
  groove, 
  continued 
  under 
  the 
  beaks. 
  Hiuge-plate 
  and 
  teeth 
  

   rather 
  strong; 
  the 
  anterior 
  series 
  of 
  teeth 
  the 
  shorter, 
  forming 
  a. 
  

   marked 
  angle 
  with 
  the 
  posterior 
  series. 
  Eesiliuui 
  supported 
  by 
  a 
  rela- 
  

   tively 
  large 
  and 
  strong 
  chondrophore, 
  placed 
  on 
  the 
  surface 
  of 
  the 
  

   hinge 
  plate, 
  distinctly 
  behind 
  the 
  beaks 
  and 
  at 
  the 
  proximal 
  end 
  of 
  the 
  

   posterior 
  series 
  of 
  teeth. 
  • 
  Pallia! 
  line 
  indistinct. 
  

  

  The 
  curious 
  little 
  shell 
  for 
  which 
  this 
  genus 
  is 
  proposed 
  is 
  remarkable 
  

   for 
  its 
  form 
  and 
  the 
  size 
  and 
  position 
  of 
  the 
  cartilage 
  and 
  chondro- 
  

   phore, 
  as 
  well 
  as 
  for 
  its 
  few 
  blunt 
  teeth. 
  If 
  we 
  are 
  correct 
  in 
  our 
  con- 
  

   clusions 
  as 
  to 
  the 
  anterior 
  and 
  posterior 
  ends, 
  the 
  beaks 
  turn 
  forward 
  

   as 
  in 
  Tindaria. 
  The 
  i)rincipal 
  reason 
  for 
  considering 
  the 
  longer 
  end 
  

   posterior 
  is 
  the 
  existence 
  of 
  a 
  well-formed 
  ligament 
  and 
  groove 
  along 
  

   that 
  end 
  and 
  not 
  on 
  the 
  shorter 
  one. 
  

  

  MICROYOLDIA 
  REGULARIS 
  (Verrill). 
  

  

  (Plate 
  LXXVIII, 
  figs. 
  5, 
  6.) 
  

  

  Yoldia 
  reynlaris 
  Verkill, 
  Trans. 
  Conu. 
  Acad., 
  VI, 
  pp. 
  228, 
  279, 
  1884. 
  

   Mlcroyoldia 
  regularis 
  Verrill 
  and 
  Bush, 
  Amer. 
  Jonru. 
  Sci., 
  Ill, 
  p. 
  56, 
  figs. 
  5,6, 
  

   January, 
  1897. 
  

  

  This 
  sj)ecies 
  closely 
  resembles 
  the 
  very 
  young 
  of 
  Megayoldia 
  thracice- 
  

   formis 
  (Storer) 
  Yerrill 
  and 
  Bush, 
  in 
  the 
  character 
  of 
  the 
  hinge. 
  Speci- 
  

   mens 
  of 
  the 
  latter 
  measuring 
  3.5 
  mm. 
  in 
  length 
  have 
  the 
  relatively 
  

   large, 
  concave, 
  cartilage 
  plate 
  just 
  before 
  the 
  beaks, 
  which 
  curve 
  

   strongly 
  backward 
  and 
  are 
  nearer 
  the 
  center 
  of 
  the 
  shell, 
  and 
  the 
  teeth 
  

   are 
  more 
  numerous 
  and 
  more 
  slender. 
  

  

  In 
  M. 
  regularis 
  the 
  shell 
  is 
  cordate 
  ovate 
  or 
  veneriform. 
  The 
  beaks 
  

   curve 
  strongly 
  toward 
  the 
  short 
  (anterior 
  ?) 
  end. 
  There 
  is 
  on 
  this 
  end 
  

   a 
  sunken 
  lunular 
  area 
  defined 
  by 
  a 
  slight 
  groove 
  which 
  indents 
  the 
  

   hinge-margin. 
  The 
  anterior 
  ( 
  ?) 
  part 
  of 
  the 
  hinge-margin 
  is 
  thickened 
  

   and 
  incurved 
  along 
  the 
  luuule 
  and 
  bears 
  an 
  inner 
  ridge 
  and 
  four 
  or 
  live, 
  

   small, 
  blunt 
  teeth 
  of 
  which 
  the 
  proximal 
  two 
  x^roject 
  above 
  the 
  margin 
  

   in 
  a 
  dorsal 
  view, 
  the 
  others 
  are 
  low 
  and 
  rather 
  obscure. 
  Under 
  the 
  

   beak 
  the 
  hinge-plate 
  is 
  thickened, 
  sinuous, 
  edentulous 
  for 
  a 
  short 
  dis- 
  

   tance; 
  back 
  ( 
  ?) 
  of 
  this 
  there 
  is 
  a 
  large, 
  thick, 
  oblique, 
  concave 
  chon- 
  

   drophore 
  which 
  occupies 
  the 
  whole 
  breadth 
  of 
  the 
  hinge-margin 
  and 
  

   l)roJects 
  inward 
  beyond 
  it 
  as 
  a 
  shelf-like 
  border; 
  beyond 
  this 
  there 
  is 
  a 
  

   series 
  of 
  six 
  or 
  seven 
  prominent, 
  blunt 
  teeth. 
  The 
  external 
  ligament 
  

   lies 
  in 
  a 
  distinct 
  grove 
  along 
  a 
  large 
  part 
  of 
  the 
  edge 
  of 
  the 
  longer 
  

   (posterior?) 
  dorsal 
  margin 
  and 
  runs 
  under 
  the 
  beak, 
  but 
  fades 
  out 
  in 
  

   front 
  of 
  it. 
  The 
  pallial 
  sinus 
  is 
  not 
  visible, 
  consequently 
  it 
  is 
  not 
  

   possible 
  to 
  decide 
  which 
  is 
  the 
  anterior 
  end. 
  

  

  