﻿1000 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  Nucleospira, 
  Hall. 
  1859. 
  

   (Plate 
  38, 
  figs. 
  21-38.) 
  

  

  Shells 
  usually 
  small; 
  subcircular 
  in 
  outline, 
  

   equally 
  convex, 
  often 
  gibbous 
  or 
  ventricose. 
  

  

  Yalves 
  sub- 
  

   Hinge-line 
  

  

  very 
  short, 
  cardinal 
  extremities 
  rounded. 
  On 
  the 
  pedicle- 
  

   valve 
  the 
  cardinal 
  area 
  is 
  low 
  and 
  obscurt 
  d 
  by 
  the 
  incurvature 
  

   of 
  the 
  beak. 
  Only 
  in 
  very 
  young 
  specimens 
  is 
  the 
  deltidium 
  

  

  Fig. 
  380. 
  

  

  FIG.S881. 
  

  

  Fig. 
  383. 
  

  

  Fig. 
  380. 
  — 
  A 
  preparation 
  of 
  Nucleospira 
  ventricosa, 
  Hall; 
  showing 
  the 
  umbonal 
  blades, 
  the 
  

  

  jugum 
  and 
  the 
  form 
  of 
  the 
  first 
  volution 
  of 
  the 
  spirals. 
  

   Figs. 
  381, 
  382.— 
  The 
  primary 
  lamellae 
  and 
  jugum 
  of 
  Nucleospira 
  ventricosa, 
  Hall. 
  

   Fig. 
  883 
  — 
  A 
  preparation 
  of 
  Nucleospira 
  concinna, 
  Hall; 
  showing 
  one-half 
  of 
  the 
  brachidium, 
  

  

  the 
  mode 
  of 
  attachment 
  of 
  the 
  crura 
  to 
  the 
  umbonal 
  blades 
  and 
  the 
  flattened 
  

  

  stem 
  of 
  the 
  jugum. 
  

  

  exposed, 
  and 
  it 
  then 
  consists 
  of 
  two 
  plates 
  attached 
  to 
  the 
  lateral 
  

   margins 
  of 
  the 
  delthyrium; 
  in 
  mature 
  individuals 
  these 
  plates 
  

   are 
  coalesced 
  and 
  incurved, 
  the 
  median 
  suture 
  is 
  lost 
  and 
  the 
  

   foramen 
  covered 
  ; 
  the 
  appearance 
  of 
  the 
  deltidium 
  is 
  that 
  of 
  a 
  

   triangular 
  concave 
  plate, 
  limited 
  by 
  rather 
  sharp 
  dental 
  ridges 
  

   and 
  covering 
  the 
  delthyrium 
  for 
  about 
  half 
  its 
  length. 
  The 
  

   teeth 
  are 
  prominent, 
  approximate, 
  recurved 
  at 
  the 
  tips, 
  supported 
  

   by 
  thickened 
  bases 
  but 
  not 
  by 
  lamellae. 
  Dental 
  sockets 
  very 
  

  

  58 
  

  

  