﻿FROM 
  THE 
  LOWER 
  SILURIAN 
  OE 
  NORTH 
  AMERICA. 
  507 
  

  

  the 
  generally 
  greater 
  number 
  of 
  the 
  minute 
  intermediate 
  tubules, 
  

   the 
  tuberculated 
  margins 
  of 
  the 
  calices, 
  and 
  the 
  existence 
  of 
  the 
  

   curious 
  stellate, 
  solid 
  or 
  porous 
  interspaces. 
  The 
  value 
  of 
  this 
  last 
  

   character 
  is 
  diminished 
  by 
  the 
  fact 
  that 
  some 
  specimens, 
  otherwise 
  

   the 
  same, 
  do 
  not 
  exhibit 
  these 
  spaces 
  in 
  a 
  conspicuous 
  manner. 
  

   The 
  tuberculated 
  margins 
  of 
  the 
  calices, 
  though 
  this 
  feature 
  can 
  

   only 
  be 
  detected 
  with 
  the 
  use 
  of 
  a 
  high 
  magnifying-power, 
  remind 
  

   one 
  of 
  the 
  species 
  generally 
  considered 
  as 
  belonging 
  to 
  the 
  genus 
  

   Stenopora. 
  

  

  Locality 
  and 
  Formation. 
  Not 
  rare 
  in 
  the 
  Cincinnati 
  group, 
  near 
  

   Cincinnati, 
  Ohio. 
  Collected 
  by 
  Mr. 
  TJ. 
  P. 
  James. 
  

  

  11. 
  ClOETETES 
  RHOMBICTTS, 
  Nich. 
  PI. 
  XXIX. 
  figS. 
  11-116. 
  

  

  Corallum 
  ramose, 
  the 
  branches 
  solid 
  or 
  hollow, 
  subcylindrical, 
  

   from 
  4 
  to 
  5 
  lines 
  in 
  diameter, 
  terminating 
  in 
  acutely 
  pointed, 
  or 
  at 
  

   other 
  times 
  swollen 
  and 
  bulbous, 
  extremities. 
  Corallites 
  with 
  very 
  

   thin 
  walls, 
  about 
  eight 
  or 
  ten 
  in 
  the 
  space 
  of 
  one 
  line, 
  variable 
  in 
  

   form 
  and 
  arrangement. 
  In 
  parts 
  of 
  the 
  corallum 
  the 
  calices 
  are 
  

   regularly 
  hexagonal 
  ; 
  but 
  over 
  the 
  greater 
  portion 
  of 
  the 
  surface 
  

   they 
  are 
  obliquely 
  rhombic, 
  and 
  are 
  arranged 
  in 
  regular 
  diagonal 
  

   rows, 
  the 
  direction 
  of 
  which, 
  however, 
  changes 
  within 
  short 
  dis- 
  

   tances, 
  giving 
  to 
  the 
  corallum 
  a 
  most 
  peculiar 
  appearance. 
  In 
  any 
  

   given 
  portion 
  of 
  the 
  surface 
  in 
  which 
  this 
  arrangement 
  obtains, 
  the 
  

   calices 
  are 
  disposed 
  in 
  a 
  double 
  series 
  of 
  diagonals, 
  the 
  one 
  set 
  

   crossing 
  the 
  branch 
  more 
  or 
  less 
  transversely, 
  whilst 
  those 
  of 
  the 
  

   other 
  set 
  have 
  a 
  direction 
  more 
  or 
  less 
  corresponding 
  with 
  the 
  axis 
  of 
  

   the 
  stem. 
  The 
  corallites 
  are 
  nearly 
  equal 
  in 
  size 
  ; 
  and 
  there 
  are 
  no 
  

   very 
  minute 
  tubuli 
  interspersed 
  amongst 
  the 
  average 
  tubes. 
  Occa- 
  

   sionally 
  a 
  corallite 
  may 
  be 
  slightly 
  larger 
  than 
  the 
  average 
  ; 
  but 
  

   the 
  surface 
  exhibits 
  no 
  tubercles, 
  or 
  regular 
  groups 
  of 
  large-sized 
  

   corallites. 
  

  

  The 
  present 
  species 
  is 
  related 
  in 
  some 
  degree 
  to 
  Chcetetes 
  (Monti- 
  

   culipora) 
  Boiverbanki, 
  Edw. 
  & 
  H. 
  ; 
  but 
  it 
  differs 
  altogether 
  in 
  its 
  

   mode 
  of 
  growth, 
  especially 
  when 
  young, 
  whilst 
  the 
  calices 
  are 
  only 
  

   about 
  half 
  as 
  large. 
  , 
  . 
  

  

  Locality 
  and 
  Formation. 
  Cincinnati 
  group, 
  near 
  Cincinnati, 
  

   Ohio. 
  Collected 
  by 
  Mr. 
  TJ. 
  P. 
  James. 
  

  

  II. 
  Frondescent 
  and 
  Palmate 
  Species. 
  

  

  The 
  species 
  of 
  this 
  group 
  of 
  the 
  genus 
  Chcetetes 
  have 
  a 
  corallum 
  

   which 
  forms 
  a 
  flattened 
  or 
  undulated, 
  often 
  palmate 
  or 
  subpalmate 
  

   expansion, 
  of 
  small 
  thickness, 
  but 
  often 
  attaining 
  a 
  considerable 
  

   width 
  and 
  height. 
  The 
  corallum 
  is 
  composed 
  primitively 
  of 
  two 
  

   layers 
  of 
  corallites, 
  the 
  bases 
  of 
  which 
  are 
  in 
  contact, 
  and 
  which 
  are 
  

   directed 
  in 
  opposite 
  directions 
  from 
  a 
  common 
  calcareous 
  membrane. 
  

   The 
  corallum 
  is 
  rooted 
  at 
  the 
  base, 
  with 
  which 
  exception 
  the 
  entire 
  

   surface 
  is 
  covered 
  by 
  the 
  calices 
  on 
  both 
  sides. 
  In 
  old 
  examples, 
  

   additional 
  strata 
  of 
  corallites 
  may 
  be 
  superimposed 
  upon 
  the 
  two 
  

   primitive 
  layers. 
  

  

  