﻿62 
  Verrill 
  and 
  Bush 
  — 
  Genera 
  of 
  Zedidce 
  and 
  Nuculidm. 
  

  

  d. 
  Shell 
  elongated 
  and 
  tapered 
  posteriously, 
  rostrum 
  long, 
  

  

  bicarinate, 
  blunt, 
  ligamental 
  area 
  or 
  escutcheon 
  

   long 
  and 
  well-defined 
  ; 
  pallial 
  sinus 
  and 
  siphon 
  tubes 
  

  

  developed 
  Leda 
  (sens, 
  rest.) 
  

  

  dd. 
  Shell 
  shorter, 
  swollen, 
  ovate 
  or 
  oblong, 
  posteriorly 
  not 
  much 
  

   elongated 
  ; 
  rostrum 
  short, 
  usually 
  acute, 
  unicarinate. 
  

  

  e. 
  Shell 
  ovate, 
  rostrum 
  small 
  acute 
  ; 
  ligamentary 
  area 
  or 
  

  

  escutcheon 
  distinctly 
  bordered 
  by 
  a 
  carina. 
  

  

  f. 
  Rostrum 
  short, 
  sub-acute, 
  sub-median, 
  defined 
  below 
  by 
  a 
  

  

  ventral-sinuosity 
  or 
  emargination. 
  

  

  Ledella, 
  nov.=Junonia 
  Seguenza. 
  

   ff. 
  Rostrum 
  short, 
  dorsal, 
  not 
  defined 
  below 
  by 
  a 
  ventral 
  sinu- 
  

   osity; 
  postero-dorsal 
  margin 
  concave; 
  escutcheon 
  

   sunken 
  Jupiteria 
  Bellardi. 
  

  

  ee. 
  Shell 
  oblong, 
  angular, 
  subtruncate, 
  rostrum 
  short, 
  angular, 
  

   dorsal, 
  defined 
  below 
  by 
  a 
  marginal 
  sinuosity 
  ; 
  escutch- 
  

   eon 
  well 
  defined 
  Portlandia 
  Morch. 
  

  

  cc. 
  Shell 
  not 
  rostrated, 
  small, 
  ovate 
  or 
  elliptical, 
  rounded 
  at 
  

   both 
  ends, 
  anterior 
  end 
  the 
  shorter, 
  no 
  carina, 
  lunule, 
  

   nor 
  escutcheon 
  ; 
  cartilage 
  posterior, 
  internymphal. 
  

  

  Microyoldia, 
  nov. 
  

  

  bb. 
  Shell 
  oblong 
  or 
  lanceolate, 
  compressed, 
  nearly 
  plain, 
  more 
  

   or 
  less 
  gaping 
  at 
  both 
  ends 
  ; 
  rostrum 
  not 
  well 
  defined 
  ; 
  

   pallial 
  sinus 
  large 
  and 
  broad 
  ; 
  tubes 
  long, 
  united. 
  

  

  g. 
  Teeth 
  transverse, 
  v-shaped, 
  numerous, 
  in 
  two 
  long 
  series 
  ; 
  

   chondrophore 
  large, 
  concave, 
  projecting 
  strongly 
  inside 
  

   the 
  hinge-plate 
  Yoldia 
  Moller 
  (sens, 
  ext.) 
  

  

  h. 
  Shell 
  large, 
  compressed, 
  rounded 
  anteriorly, 
  broadest 
  pos- 
  

   teriorly 
  with 
  a 
  postero-ventral 
  protrusion 
  and 
  radial 
  

   ridge 
  ; 
  rostrum 
  short, 
  broad, 
  poorly 
  defined 
  ; 
  external 
  

   ligament 
  well-developed, 
  prominent 
  both 
  sides 
  of 
  the 
  

   beaks, 
  occupying 
  a 
  continuous 
  furrow 
  ; 
  no 
  lunule 
  nor 
  

   escutcheon 
  Megayoldia, 
  nov. 
  

  

  hh. 
  Shell 
  lanceolate 
  or 
  long-ovate, 
  posteriorly 
  narrowed 
  and 
  

   somewhat 
  elongated, 
  more 
  or 
  less 
  sinuous 
  below 
  ; 
  ros- 
  

   trum 
  slightly 
  defined, 
  smooth 
  or 
  slightly 
  carinate 
  ; 
  

   external 
  ligament 
  feebly 
  developed 
  ..Yoldia 
  (sens, 
  rest.) 
  

  

  hhh. 
  Shell 
  oblong, 
  smooth, 
  plain, 
  blunt 
  and 
  rounded 
  at 
  both 
  

   ends, 
  without 
  any 
  distinct 
  carina, 
  sinuosity 
  or 
  rostrum. 
  

  

  Orthoyoldia, 
  nov. 
  

  

  hhhh. 
  Shell 
  thin, 
  compressed, 
  narrow 
  lanceolate 
  or 
  long 
  elliptical, 
  

   nearly 
  equilateral, 
  and 
  gaping 
  at 
  both 
  ends. 
  

  

  Adrana 
  H. 
  and 
  A. 
  Ad. 
  

  

  gg. 
  Shell 
  thin, 
  oblong, 
  inequilateral, 
  blunt 
  at 
  both 
  ends, 
  not 
  

   rostrated 
  nor 
  carinated 
  ; 
  teeth 
  few, 
  lamellar, 
  very 
  

   oblique. 
  Type 
  S. 
  frag 
  His 
  Jeffreys 
  Silicula 
  Jeffreys. 
  

  

  aa. 
  Shell 
  small, 
  nearly 
  plain, 
  not 
  much 
  rostrated 
  nor 
  carina- 
  

   ted 
  ; 
  cartilage 
  without 
  a 
  prominent 
  chondrophore, 
  sit- 
  

   uated 
  in 
  a 
  notch 
  in 
  the 
  hinge-margin, 
  interrupting 
  the 
  

   series 
  of 
  teeth. 
  

  

  