﻿Report 
  of 
  tee 
  State 
  Geologist. 
  

  

  975 
  

  

  jugum 
  is 
  neither 
  divided 
  nor 
  pectinated, 
  while 
  the 
  spiral 
  ribbon 
  

   bears 
  short 
  spinules 
  on 
  the 
  edge 
  and 
  face 
  of 
  the 
  lamellae 
  fronting 
  

   the 
  sides 
  of 
  the 
  shell. 
  

  

  (Type, 
  Actinooonohus 
  planosulcatus, 
  Phillips 
  (sp.). 
  Carbon- 
  

   iferous.) 
  

  

  Subgenus 
  Seminula, 
  McCoy. 
  1844. 
  

   (Plate 
  35, 
  figs. 
  11-19.) 
  

  

  Shells 
  transverse, 
  often 
  elongate 
  or 
  ficiform; 
  valves 
  biconvex, 
  

   the 
  pedicle-valve 
  with 
  a 
  median 
  sinus 
  over 
  the 
  pallial 
  region, 
  

   and 
  the 
  brachial 
  valve 
  with 
  a 
  corresponding 
  ridge 
  ; 
  both 
  sinus 
  

   and 
  fold 
  may 
  be 
  divided 
  by 
  a 
  sharp 
  median 
  sulcus 
  extending 
  

   from 
  the 
  umbones 
  to 
  the 
  margins. 
  There 
  is 
  frequently 
  

   evidence 
  of 
  a 
  single 
  obscure 
  lateral 
  fold 
  on 
  each 
  side 
  of 
  both 
  

   valves. 
  The 
  umbo 
  of 
  the 
  pedicle-valve 
  is 
  incurved 
  and 
  the 
  del- 
  

   tidial 
  area 
  is 
  usually 
  concealed 
  ; 
  the 
  foramen, 
  however, 
  is 
  exposed 
  

  

  Figs. 
  313, 
  314. 
  — 
  The 
  jugum 
  of 
  Seminula 
  subtilita, 
  Hall. 
  

  

  as 
  a 
  circular 
  or 
  ovate 
  aperture 
  which 
  encroaches 
  on 
  the 
  substance 
  

   of 
  the 
  valve. 
  In 
  the 
  pedicle-valve 
  the 
  diductor 
  muscular 
  impres- 
  

   sions 
  are 
  very 
  faintly 
  denned 
  ; 
  the 
  adductor 
  and 
  pedicle 
  impres- 
  

   sions 
  are 
  as 
  in 
  the 
  typical 
  forms 
  of 
  Athykis. 
  In 
  the 
  brachial 
  valve 
  

   the 
  hinge-plate 
  is 
  highly 
  developed, 
  its 
  upper 
  face 
  being 
  subquad- 
  

   rate 
  in 
  outline, 
  concave 
  on 
  the 
  surface, 
  the 
  concavity 
  deepening 
  

   toward 
  the 
  visceral 
  foramen 
  which 
  lies 
  just 
  beneath 
  the 
  beak 
  ; 
  

   not 
  infrequently 
  the 
  foramen 
  is 
  closed 
  by 
  secretions 
  of 
  testaceous 
  

   matter. 
  The 
  posterior 
  flanges 
  of 
  the 
  plate 
  pass 
  beyond 
  the 
  hinge- 
  

   line 
  and 
  into 
  the 
  umbonal 
  cavity 
  of 
  the 
  opposite 
  valve. 
  The 
  

   anterior 
  face 
  of 
  the 
  plate 
  is 
  erect 
  and 
  the 
  anterior 
  edge 
  somewhat 
  

  

  33 
  

  

  