﻿Verrill 
  and 
  Bash 
  — 
  Genera 
  of 
  Ledidce 
  and 
  Nuculidaa. 
  55 
  

  

  <etc., 
  it 
  agrees 
  more 
  nearly 
  with 
  the 
  former, 
  but 
  in 
  general 
  outline, 
  

   with 
  the 
  latter. 
  

  

  Yoldia 
  Moller. 
  Figures 
  12, 
  16. 
  Type 
  Y. 
  hyperborea 
  Torrell. 
  

  

  We 
  propose 
  to 
  restrict 
  this 
  genus 
  to 
  the 
  typical 
  forms, 
  such 
  as 
  

   limatula 
  (Say) 
  (fig. 
  12), 
  sapotilla 
  (Gld.) 
  (fig. 
  16), 
  myalls 
  (Couth.) 
  

   and 
  many 
  closely 
  allied 
  foreign 
  species. 
  

  

  These 
  have 
  a 
  nearly 
  smooth, 
  compressed, 
  lanceolate, 
  gaping 
  

   shell, 
  more 
  or 
  less 
  prolonged 
  and 
  tapered 
  posteriorly, 
  with 
  a 
  

   poorly 
  defined 
  wide 
  rostrum, 
  generally 
  without 
  carinations. 
  The 
  

   external 
  ligament 
  is 
  marginal, 
  feebly 
  developed, 
  continuous 
  under 
  

   the 
  beaks, 
  and 
  not 
  much 
  differentiated 
  from 
  the 
  general 
  epidermis. 
  

   The 
  chondrophore 
  is 
  large, 
  concave, 
  and 
  projects 
  within 
  the 
  

   margin. 
  The 
  pallial 
  sinus 
  is 
  large 
  and 
  deep. 
  The 
  siphon-tubes 
  

   and 
  posterior 
  pallial 
  tentacle 
  are 
  long. 
  The 
  palpal 
  tentacles 
  are 
  

   long 
  and 
  tapered 
  ; 
  in 
  life 
  they 
  may 
  extend 
  nearly 
  to 
  the 
  end 
  of 
  

   the 
  expanded 
  siphon. 
  

  

  Orthoyoldia, 
  gen. 
  nov. 
  Type 
  Orthoyoldia 
  scapina 
  (Dall). 
  

  

  Shell 
  oblong, 
  gaping, 
  blunt 
  or 
  rounded 
  at 
  both 
  ends, 
  without 
  

   distinct 
  rostrum; 
  no 
  carina. 
  Pallial 
  sinus 
  large 
  and 
  broad. 
  

   Teeth 
  numerous 
  in 
  both 
  series. 
  0. 
  scapina 
  (Dall), 
  from 
  off 
  Brazil, 
  

   and 
  0. 
  solenoides 
  (Dall), 
  from 
  the 
  West 
  Indies. 
  

  

  Megai/oldia, 
  gen. 
  nov. 
  Figure 
  17. 
  Type 
  31. 
  thraciceformis 
  

  

  (Storer). 
  

  

  Shell 
  large, 
  compressed, 
  gaping, 
  with 
  a 
  very 
  short, 
  blunt, 
  

   indefinite, 
  postero-dorsal 
  rostrum. 
  A 
  low 
  radial 
  ridge, 
  ends 
  in 
  a 
  

   postero-ventral 
  marginal 
  lobe. 
  A 
  well 
  defined 
  but 
  thin 
  external 
  

   marginal 
  ligament 
  extends 
  both 
  before 
  and 
  hehind 
  the 
  beaks, 
  

   anteriorly 
  with 
  a 
  supramarginal 
  furrow. 
  

  

  The 
  chondrophore 
  is 
  remarkably 
  large 
  and 
  strong, 
  concave, 
  

   striated 
  within, 
  and 
  projects 
  much 
  within 
  the 
  margin 
  of 
  the 
  hinge- 
  

   plate. 
  The 
  pallial 
  sinus 
  is 
  large 
  and 
  deep. 
  

  

  The 
  postero-ventral 
  margin 
  of 
  the 
  mantle 
  forms 
  a 
  pouch-like 
  

   protrusion, 
  corresponding 
  to 
  the 
  radial 
  ridge. 
  The 
  siphon 
  tubes 
  

   are 
  long 
  and 
  united; 
  the 
  posterior 
  pallial 
  tentacle 
  is 
  long 
  and 
  

   slender. 
  The 
  palpi 
  are 
  very 
  large. 
  The 
  palpal 
  tentacles 
  origi- 
  

   nate 
  from 
  the 
  body 
  wall 
  at 
  the 
  base 
  of 
  the 
  outer 
  palpi 
  ; 
  they 
  are 
  

   long 
  and 
  thick, 
  with 
  a 
  large 
  furrow 
  on 
  one 
  side. 
  

  

  Yoldiella, 
  gen. 
  nov. 
  Figures 
  3, 
  4, 
  11, 
  14. 
  Type 
  Yoldiella 
  

   lucida 
  (Loven). 
  

  

  This 
  group 
  includes 
  a 
  large 
  number 
  of 
  small, 
  mostly 
  deep-sea 
  

   species, 
  with 
  glossy, 
  iridescent, 
  ovate, 
  and 
  usually 
  wedge-shaped 
  

   shells, 
  nearly 
  always 
  having 
  a 
  slight 
  postero-ventral 
  sinuosity, 
  

  

  