﻿NIAGARA 
  FALLS 
  AND 
  VICINITY 
  1 
  83 
  

  

  subauriculate; 
  cardinal 
  areas 
  narrow, 
  sometimes 
  obscurely 
  crenu- 
  

   lated 
  on 
  the 
  margins. 
  Delthyrium 
  partially 
  closed 
  by 
  convex 
  plate, 
  

   but 
  mostly 
  occupied 
  by 
  cardinal 
  process 
  of 
  opposite 
  valve. 
  Car- 
  

   dinal 
  process 
  appears 
  trilobate. 
  Muscular 
  areas 
  moderately 
  well 
  

   defined. 
  

  

  Plectambonites 
  sericea 
  (Sowerby) 
  (Fig. 
  89). 
  Leptaena 
  

   sericea 
  Hall 
  (1852. 
  Pal. 
  N. 
  Y. 
  

   2:S9, 
  pi. 
  21) 
  

  

  Distinguishing 
  characters. 
  Outline 
  

  

  

  semicircular 
  to 
  semioval; 
  hinge 
  line 
  ex- 
  

   tended, 
  ending 
  in 
  acute 
  points; 
  striae 
  Fig. 
  89 
  piectambomtes 
  sericea 
  

   strong, 
  elevated, 
  alternating 
  with 
  finer 
  ones. 
  

  

  Found 
  in 
  the 
  lower 
  Clinton 
  limestone 
  at 
  Niagara. 
  Rare. 
  

  

  Plectambonites 
  traiisversalis 
  (Wahlenberg) 
  (Fig. 
  90). 
  Lep- 
  

   taena 
  transversalis 
  Hall 
  (1852. 
  Fal. 
  N'. 
  Y. 
  2 
  :2c^6, 
  pi. 
  

  

  53. 
  fig- 
  5a-b) 
  

  

  Distinguishing 
  characters. 
  Out- 
  

   line 
  semicircular; 
  strongly 
  convex 
  

   pedicle, 
  and 
  extremely 
  concave 
  bra- 
  

   chial 
  valve, 
  conforming 
  to 
  each 
  other; 
  

   strongly 
  incurved 
  beak 
  of 
  pedicle 
  

   valve, 
  which 
  causes 
  an 
  inflection 
  of 
  

   the 
  hinge 
  line; 
  hinge 
  line 
  produced; 
  

  

  Fig. 
  90 
  Plectambonites 
  transversalis 
  ^ 
  ,. 
  , 
  , 
  , 
  . 
  . 
  . 
  

  

  fine 
  distant 
  elevated 
  striae 
  with 
  ex- 
  

   tremely 
  fine 
  striae 
  between; 
  strongly 
  punctate 
  character 
  of 
  ex- 
  

   foliated 
  portions. 
  

  

  Found 
  in 
  the 
  Clinton 
  lenses, 
  and 
  abundantly 
  in 
  the 
  lower 
  Roches- 
  

   ter 
  shale 
  at 
  Niagara. 
  Also 
  at 
  Lockport 
  (Hall). 
  

  

  Genus 
  orthothetes 
  Fischer 
  de 
  Waldheim 
  

  

  [Ety. 
  : 
  o>^o?, 
  straight] 
  

  

  (1830. 
  Sac. 
  imp. 
  natural, 
  d. 
  MoscozvBul. 
  1:375. 
  Hall 
  & 
  Clarke, 
  

   1892; 
  Pal. 
  N. 
  Y. 
  V. 
  8, 
  pt 
  I, 
  p. 
  253) 
  

  

  Shell 
  varying 
  from 
  plano-convex 
  to 
  biconvex, 
  sometimes 
  becom- 
  

   ing 
  concavo-convex 
  with 
  age. 
  Pedicle 
  valve 
  most 
  convex 
  about 
  

   the 
  beak, 
  which 
  often 
  tends 
  toward 
  irregular 
  growth; 
  cardinal 
  area 
  

   well 
  developed, 
  with 
  a 
  thick, 
  more 
  or 
  less 
  convex 
  deltidium. 
  Teeth 
  

   not 
  supported 
  by 
  dental 
  plates. 
  Brachial 
  valve 
  mo6t 
  convex 
  near 
  

  

  