﻿Report 
  of 
  the 
  State 
  Geologist. 
  845 
  

  

  verse 
  delthyrial 
  plate 
  is 
  thin 
  and 
  is 
  developed 
  into 
  a 
  delicate 
  

   though 
  distinct 
  tube. 
  Shell 
  substance 
  highly 
  punctate 
  on 
  the 
  

   inner 
  laminae. 
  Height 
  of 
  original 
  specimen, 
  13 
  mm.; 
  cardinal 
  

   width, 
  18 
  mm.; 
  length, 
  15 
  mm. 
  

  

  Choteau 
  limestone. 
  Choteau 
  Springs, 
  Missouri. 
  

  

  Amboccelia 
  spinosa, 
  sp. 
  nov. 
  

   (Plate 
  xxxix, 
  figs. 
  16-18.) 
  

  

  Shell 
  of 
  rather 
  large 
  size, 
  hinge-line 
  straight, 
  equaling 
  the 
  full 
  

   diameter 
  of 
  the 
  valve. 
  Brachial 
  valve 
  depressed 
  convex 
  in 
  the 
  

   umbonal 
  region, 
  concave 
  anteriorly, 
  with 
  upturned 
  margins. 
  

   Medially 
  there 
  is 
  a 
  low 
  and 
  indistinct 
  elevation 
  which 
  disappears 
  

   toward 
  the 
  front. 
  Pedicle-valve 
  not 
  known. 
  Surface 
  bearing 
  

   faint 
  traces 
  of 
  concentric 
  lines 
  and 
  covered 
  with 
  numerous 
  

   elongate 
  depressions 
  which 
  were 
  probably 
  bases 
  of 
  insertion 
  of 
  

   epidermal 
  spinules. 
  

  

  Length 
  of 
  original 
  specimen, 
  7 
  mm.; 
  width 
  on 
  the 
  hinge, 
  9 
  mm. 
  

  

  Hamilton 
  shales. 
  Livonia 
  Salt 
  Shaft, 
  Livingston 
  county 
  ^N. 
  Y. 
  

  

  Seminula 
  Rogersi, 
  sp. 
  nov. 
  

   (Plate 
  xlvii, 
  figs. 
  1-4.) 
  

  

  Shell 
  rather 
  small, 
  suboval 
  in 
  outline. 
  Yalves 
  subequally 
  con- 
  

   vex. 
  Pedicle-valve 
  with 
  a 
  low, 
  broad 
  median 
  sinus 
  and 
  brachial 
  

   valve 
  with 
  a 
  corresponding 
  fold, 
  both 
  becoming 
  more 
  distinct 
  

   toward 
  the 
  anterior 
  margin. 
  Lateral 
  slopes 
  depressed 
  convex. 
  

   Umbones 
  not 
  conspicuous 
  ; 
  deltidium 
  concealed. 
  

  

  External 
  surface 
  smooth. 
  

  

  A 
  normal 
  individual 
  measures 
  15 
  mm. 
  in 
  length, 
  and 
  13 
  mm. 
  in 
  

   greatest 
  width. 
  

  

  Pendleton 
  sandstone 
  (Schoharie 
  grit). 
  Pendleton, 
  Lndiana. 
  

  

  Athyris 
  densa, 
  sp. 
  nov. 
  

   (Plate 
  xlvi, 
  figs. 
  6-12.) 
  

  

  Shell 
  transversely 
  elongate, 
  valves 
  compressed 
  ; 
  median 
  fold 
  

   and 
  sinus 
  not 
  conspicuously 
  developed. 
  Pedicle-valve 
  shallow, 
  

   with 
  broad, 
  sharply 
  angled 
  cardinal 
  slopes, 
  greatly 
  thickened 
  

   interiorly. 
  The 
  anterior 
  margin 
  is 
  frequently 
  extended 
  into 
  a 
  

   linguate 
  process 
  at 
  the 
  termination 
  of 
  the 
  median 
  sinus. 
  Brachial 
  

   valve 
  the 
  more 
  convex 
  with 
  an 
  indistinct, 
  flattened 
  and 
  some- 
  

  

  