﻿Report 
  of 
  the 
  State 
  Geologist, 
  

  

  1049 
  

  

  is 
  shortened 
  and 
  constricted, 
  forming 
  a 
  projecting 
  cardinal 
  

   spur. 
  

   (Type, 
  Orishania 
  navicella, 
  Hall. 
  Oriskany 
  sandstone.) 
  

  

  Subgenus 
  Selenella, 
  Hall. 
  1893. 
  

  

  Shells 
  with 
  biconvex 
  valves, 
  smooth 
  exterior, 
  terebratuliform 
  

  

  outline, 
  narrow 
  at 
  the 
  umbones 
  and 
  broad 
  in 
  the 
  pallial 
  region. 
  

  

  The 
  brachidium 
  is 
  similar 
  to 
  that 
  of 
  Renssel^ria 
  and 
  Cen- 
  

  

  tronella; 
  the 
  anterior 
  plate 
  broader 
  and 
  less 
  attenuate 
  than 
  in 
  

  

  Fig. 
  466. 
  Pig. 
  467. 
  Fig. 
  468. 
  

  

  Selenella 
  gracilis, 
  Hall. 
  

   Fig. 
  466. 
  Outline 
  profile 
  of 
  conjoined 
  valves. 
  

   Fig. 
  467. 
  Preparation 
  showing 
  the 
  form 
  of 
  the 
  loop. 
  

   Fig. 
  468. 
  An 
  oblique 
  view; 
  showing 
  the 
  upward 
  curvature 
  of 
  the 
  anterior 
  plate. 
  X 
  3. 
  

  

  Rensseljeria 
  and 
  without 
  the 
  central, 
  rod-like 
  posterior 
  extension, 
  

   and 
  also 
  lacks 
  the 
  median 
  ridge 
  or 
  thickening 
  along 
  the 
  sym- 
  

   physis 
  of 
  the 
  lateral 
  elements, 
  which 
  exists 
  in 
  Centronella. 
  

   (Type, 
  Selenella 
  gracilis, 
  Hall. 
  Upper 
  Helderberg 
  group.) 
  

  

  Subgenus 
  Romingerina, 
  Hall. 
  1893. 
  

   (Plate 
  52, 
  figs. 
  14, 
  15.) 
  

   Shells, 
  small 
  biconvex; 
  smooth 
  valved. 
  The 
  median 
  ridge 
  

   on 
  the 
  anterior 
  plate 
  of 
  the 
  brachidium 
  is 
  elevated 
  into 
  a 
  con- 
  

   spicuous 
  vertical 
  lamella, 
  extended 
  both 
  anteriorly 
  and 
  posteriorly, 
  

   being 
  in 
  fact 
  a 
  double 
  plate 
  produced 
  by 
  the 
  abrupt 
  deflection 
  of 
  

   each 
  lateral 
  branch 
  of 
  the 
  brachidium 
  near 
  the 
  median 
  line 
  ; 
  

   union 
  taking 
  place 
  along 
  the 
  upper 
  edge, 
  which 
  almost 
  reaches 
  

   the 
  inner 
  surface 
  of 
  the 
  pedicle-valve. 
  

  

  The 
  upper 
  edge, 
  where 
  viewed 
  from 
  the 
  side, 
  is 
  flatly 
  roof- 
  

   shaped, 
  while 
  the 
  lower 
  edge 
  describes 
  two 
  convexities, 
  the 
  

   greater 
  anterior, 
  leaving 
  a 
  notch 
  between 
  them. 
  The 
  surfaces 
  

   132 
  107 
  

  

  