﻿126 
  DR. 
  G. 
  J. 
  HTXDE 
  OX 
  AKCH^OCYATHUS 
  AXD 
  OTHEE 
  GEXEEA 
  

  

  1. 
  History 
  of 
  the 
  Genus 
  Archaeocyathus 
  and 
  allied 
  forms. 
  

  

  A[r. 
  Billings's 
  first 
  notice 
  of 
  Archceocyathus 
  appeared 
  in 
  1861, 
  in 
  

   the 
  first 
  part 
  of 
  a 
  work 
  entitled 
  ' 
  Xew 
  Species 
  of 
  Lower 
  Silurian 
  Fos- 
  

   sils.' 
  The 
  specimens 
  were 
  from 
  the 
  Potsdam 
  Limestone 
  Formation 
  

   at 
  Anse 
  au 
  Lonp, 
  Labrador 
  ; 
  they 
  were 
  regarded 
  as 
  possessing 
  some 
  

   of 
  the 
  characters 
  both 
  of 
  Corals 
  and 
  Sponges, 
  and 
  the 
  following 
  were 
  

   given 
  as 
  their 
  generic 
  characters 
  : 
  — 
  " 
  Turbinate 
  simple 
  or 
  aggregate, 
  

   cup 
  deep. 
  The 
  internal 
  structure, 
  so 
  far 
  as 
  can 
  be 
  made 
  out, 
  con- 
  

   sists 
  of 
  an 
  inner 
  wall 
  constituting 
  the 
  inner 
  surface 
  of 
  the 
  cup, 
  and 
  

   an 
  external 
  wall 
  or 
  epitheca 
  enveloping 
  the 
  whole. 
  Between 
  the 
  

   two 
  walls 
  there 
  are 
  numerous 
  radiating 
  septa, 
  the 
  interseptal 
  spaces 
  

   being 
  filled 
  with 
  poriferous 
  or 
  cellular 
  tissue. 
  It 
  is 
  highly 
  probable 
  

   that 
  the 
  inner 
  wall 
  is 
  permeated 
  by 
  pores 
  communicating 
  with 
  the 
  

   interseptal 
  tissue.'* 
  Two 
  ppecies, 
  A. 
  atlanticus 
  and 
  A. 
  mlnganensis, 
  

   were 
  included 
  in 
  the 
  genus, 
  and 
  the 
  first 
  of 
  these 
  was 
  figured. 
  

   Shortly 
  afterwards, 
  the 
  description 
  and 
  figures 
  were 
  reproduced 
  iQ 
  

   the 
  ' 
  Geology 
  of 
  Vermont,' 
  vol. 
  ii. 
  Appendix, 
  pp. 
  944—946 
  (1861). 
  

  

  In 
  1865, 
  the 
  entire 
  volume, 
  of 
  which 
  the 
  part 
  published 
  in 
  1861 
  

   was 
  only 
  a 
  fragment, 
  appeared 
  under 
  the 
  title 
  of 
  ' 
  Paleozoic 
  

   Fossils,' 
  and 
  in 
  this 
  Mr. 
  Billings 
  considerably 
  modified 
  his 
  references 
  

   to 
  Archaeocyathus. 
  A 
  new 
  name, 
  A. 
  profundus, 
  is 
  given 
  to 
  forms 
  

   previously 
  referred 
  to 
  A. 
  mlnganensis 
  ; 
  these 
  are 
  figured 
  and 
  placed 
  

   first 
  as 
  the 
  type 
  of 
  the 
  genus, 
  whilst 
  A. 
  atlanticus 
  is 
  relegated 
  to 
  a 
  

   secondary 
  position. 
  The 
  generic 
  diagnosis 
  remains 
  unaltered, 
  but 
  

   it 
  is 
  stated 
  that 
  since 
  1861 
  the 
  Author 
  had 
  discovered 
  numerous 
  

   silicified 
  spicula 
  in 
  a 
  specimen 
  of 
  A. 
  minganensls, 
  and 
  that 
  these 
  

   fossils 
  must 
  therefore 
  be 
  classified 
  amongst 
  the 
  extinct 
  tribes 
  of 
  

   sponges. 
  In 
  the 
  latter 
  part 
  of 
  the 
  volume 
  (pp. 
  354-357) 
  the 
  

   generic 
  characters, 
  as 
  illustrated 
  by 
  A. 
  minganensls, 
  are 
  again 
  re- 
  

   ferred 
  to, 
  and 
  figures 
  are 
  given 
  of 
  this 
  form 
  and 
  of 
  the 
  spicules 
  

   found 
  in 
  connexion 
  with 
  it. 
  It 
  is 
  stated 
  that 
  no 
  spicules 
  had 
  been 
  

   discovered 
  in 
  A. 
  profundus 
  and 
  A. 
  atlanticus, 
  but 
  their 
  absence 
  is 
  

   attributed 
  to 
  the 
  fact 
  that 
  no 
  silicified 
  forms 
  of 
  these 
  species 
  were 
  

   known. 
  The 
  author 
  finally 
  concludes 
  that 
  all 
  three 
  species 
  belong 
  

   to 
  one 
  generic 
  group* 
  closely 
  related 
  to 
  Calathium, 
  Bill., 
  a 
  genus 
  of 
  

   siliceous 
  sponges. 
  

  

  * 
  It 
  will 
  be 
  shown 
  in 
  the 
  sequel 
  that 
  each 
  of 
  these 
  species 
  belongs 
  to 
  a 
  dis- 
  

   tinct 
  genus 
  ; 
  and 
  the 
  question 
  then 
  arises, 
  for 
  which 
  of 
  them 
  the 
  generic 
  name 
  

   of 
  Archteoeyothus 
  should 
  be 
  retained. 
  In 
  the 
  usual 
  course 
  of 
  proceeding 
  the 
  

   species 
  first 
  described, 
  A. 
  atlanticus, 
  would 
  bear 
  the 
  generic 
  name 
  ; 
  but 
  in 
  the 
  

   reprint 
  of 
  the 
  original 
  description 
  in 
  1865, 
  the 
  author 
  removes 
  this 
  from 
  the 
  

   first 
  place, 
  and 
  substitutes 
  A. 
  profundus 
  as 
  the 
  type. 
  The 
  reason 
  for 
  this 
  is 
  

   evident. 
  One 
  of 
  the 
  main 
  features 
  in 
  the 
  diagnosis 
  of 
  ArchcBocyathus 
  is 
  the 
  

   possession 
  of 
  radiating 
  septa, 
  and 
  in 
  A. 
  atlanticus 
  such 
  structures 
  cannot 
  strictly 
  

   be 
  said 
  to 
  be 
  present, 
  whilst 
  they 
  are 
  extremely 
  well 
  marked 
  in 
  A. 
  profundus 
  ; 
  

   consequently 
  the 
  former 
  species 
  cannot 
  be 
  retained 
  in 
  the 
  genus 
  without 
  com- 
  

   pletely 
  altering 
  the 
  generic 
  characters 
  given 
  by 
  Air. 
  Billings, 
  whilst 
  these 
  fully 
  

   agree 
  with 
  A. 
  profundus. 
  Since 
  no 
  other 
  author 
  treated 
  of 
  the 
  genus 
  in 
  the 
  

   interval 
  between 
  the 
  first 
  description 
  and 
  the 
  subsequent 
  alteration 
  and 
  correc- 
  

   tion, 
  it 
  seems 
  only 
  fair 
  and 
  reasonable 
  to 
  allow 
  the 
  same 
  right 
  to 
  the 
  author, 
  to 
  

   amend 
  his 
  own 
  mistake, 
  which 
  would 
  be 
  conceded 
  to 
  an 
  independent 
  writer 
  ; 
  

   and 
  I 
  propose 
  therefore 
  to 
  adopt 
  as 
  the 
  type 
  of 
  the 
  genus 
  the 
  form 
  which 
  was 
  

   so 
  designated 
  by 
  Air. 
  Billings, 
  viz. 
  A. 
  vrofundus. 
  

  

  