﻿976 
  Forty- 
  seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  trilobed, 
  the 
  lateral 
  lobes 
  bearing 
  the 
  crural 
  bases. 
  The 
  crura 
  

   are 
  straight 
  and 
  their 
  attachment 
  to 
  the 
  primary 
  lamellae 
  is 
  of 
  

   the 
  same 
  character 
  as 
  in 
  Cliothyris, 
  etc. 
  The 
  primary 
  lamellae, 
  

   on 
  the 
  umbonal 
  curve, 
  are 
  broad, 
  the 
  jugum 
  usually 
  situated 
  

   posteriorly. 
  The 
  saddle 
  of 
  the 
  jugum 
  is 
  often 
  bilobed 
  on 
  its 
  

   anterior 
  margin, 
  and 
  frequently 
  both 
  it 
  and 
  the 
  outer 
  margins 
  of 
  

   the 
  ribbon 
  of 
  the 
  secondary 
  volutions 
  are 
  fimbriated. 
  

  

  The 
  muscular 
  impressions 
  of 
  this 
  valve 
  are 
  very 
  narrow, 
  and 
  

   subdivided 
  into 
  two 
  pairs 
  of 
  elongate 
  scars. 
  The 
  members 
  of 
  the 
  

   posterior 
  pair 
  are 
  divided 
  by 
  a 
  median 
  septum 
  or 
  ridge, 
  which 
  

   begins 
  beneath, 
  though 
  it 
  does 
  not 
  support 
  the 
  hinge-plate. 
  

   Branching 
  vascular 
  sinuses 
  are 
  sometimes 
  retained 
  over 
  the 
  

   pallial 
  region 
  of 
  both 
  valves. 
  

  

  Surface 
  of 
  the 
  valves 
  smooth, 
  that 
  is, 
  with 
  sharp, 
  concentric 
  

   striae 
  which 
  were 
  never 
  produced 
  into 
  lamellae. 
  

  

  (Type, 
  Seminula 
  ambigua, 
  Sowerby 
  (sp.). 
  Carboniferous.) 
  

  

  Subgenus 
  Spirigerella, 
  Waagen. 
  1883. 
  

  

  Shells 
  elongate 
  transverse; 
  contour 
  showing 
  a 
  decided 
  ten- 
  

   dency 
  to 
  piano-convexity, 
  the 
  pedicle-valve 
  being 
  depressed 
  by 
  a 
  

   broad, 
  flat 
  sinus, 
  and 
  the 
  brachial 
  valve 
  considerably 
  elevated 
  ; 
  

   cardinal 
  slopes 
  more 
  or 
  less 
  pronounced 
  ; 
  

   surface 
  smooth 
  or 
  with 
  sharp, 
  concentric 
  

   growth-lines, 
  which 
  were 
  not 
  produced 
  into 
  

   lamellae 
  or 
  spines. 
  On 
  the 
  interior 
  the 
  hinge- 
  

   plate 
  is 
  high, 
  the 
  anterior 
  face 
  being 
  erect, 
  

  

  Fig. 
  315— 
  Jugum 
  of 
  Spi- 
  \ 
  * 
  ' 
  . 
  & 
  ' 
  

  

  Hgereiia 
  Derbyt, 
  waagen 
  the 
  upper 
  face 
  subquadrate 
  m 
  outline 
  and 
  

   (Waagen.) 
  concave, 
  the 
  posterior 
  face 
  extending 
  con- 
  

  

  siderably 
  beyond 
  the 
  hinge 
  ; 
  it 
  is 
  perforated 
  by 
  a 
  visceral 
  fora- 
  

   men. 
  The 
  jugum 
  is 
  situated 
  pretty 
  well 
  back 
  and 
  its 
  structure 
  is 
  

   essentially 
  like 
  that 
  in 
  Actinoconchus 
  planosidcatus 
  ; 
  in 
  S. 
  Derby 
  'i, 
  

   however, 
  the 
  saddle 
  of 
  the 
  jugum, 
  which 
  is 
  entire 
  on 
  its 
  anterior 
  

   margin, 
  bears 
  a 
  median 
  septum 
  on 
  its 
  summit, 
  extending 
  

   from 
  its 
  anterior 
  edge 
  to 
  the 
  bifurcation 
  of 
  the 
  stem 
  ; 
  a 
  

   feature 
  not 
  elsewhere 
  observed 
  among 
  the 
  athyroids, 
  except 
  

   in 
  Kayserta. 
  

  

  (Type, 
  /Spirigerella 
  Derbyi, 
  Waagen. 
  (?) 
  Carboniferous.) 
  

  

  34 
  

  

  