﻿948 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  These 
  radiate 
  shells 
  may 
  be 
  conveniently 
  subdivided 
  as 
  follows 
  : 
  

  

  1. 
  JPauciplieati, 
  or 
  those 
  with 
  few 
  low 
  plications 
  ; 
  as 
  Spirifer 
  

   radiatus, 
  Sowerby, 
  S. 
  Eudora, 
  Hall, 
  from 
  the 
  Clinton 
  and 
  Niagara 
  

   faunas, 
  S. 
  macropleura, 
  Conrad, 
  from 
  the 
  Lower 
  Helderberg 
  

   group. 
  

  

  2. 
  Mulliplicati, 
  or 
  those 
  with 
  numerous 
  plications 
  ; 
  as 
  Spirifer 
  

   JViagarensis, 
  Conrad, 
  S. 
  asperatus, 
  Eingueberg, 
  of 
  the 
  Niagara 
  

   group 
  ; 
  S. 
  Tullia, 
  Hall, 
  of 
  the 
  Hamilton 
  fauna 
  ; 
  S. 
  Belphegor, 
  

   Clarke, 
  of 
  the 
  Genesee 
  shales; 
  S. 
  mesastrialis, 
  Hall, 
  of 
  the 
  

   Chemung 
  group. 
  

  

  3. 
  Dupliciplicati 
  ; 
  a 
  few 
  Upper 
  Silurian 
  species 
  having 
  strong 
  

   dichotomous 
  plications 
  and 
  the 
  filamentous 
  surface 
  striae 
  covered 
  

   with 
  asperities. 
  Such 
  are 
  Spirifer 
  nobilis, 
  Barrande, 
  from 
  the 
  

   etage 
  E 
  2 
  , 
  and 
  the 
  Niagara 
  limestone 
  of 
  Illinois 
  and 
  Wisconsin, 
  

   and 
  S. 
  Schmidti, 
  Lindstrom, 
  from 
  the 
  Gotland 
  limestone. 
  

  

  Section 
  II. 
  Lamellosi. 
  (Plate 
  24, 
  figs. 
  1-20.) 
  Typical 
  examples, 
  

   Spirifer 
  perlamellosus, 
  Hall, 
  S. 
  mueronatus, 
  Conrad. 
  

  

  Kadially 
  plicated 
  ; 
  surface 
  covered 
  with 
  numerous 
  concentric 
  

   lamellae. 
  In 
  Silurian 
  species 
  the 
  fold 
  and 
  sinus 
  are 
  non- 
  plicate 
  ; 
  

   the 
  later 
  forms 
  usually 
  bear 
  a 
  low 
  median 
  depression 
  on 
  the 
  fold 
  

   accompanied 
  by 
  a 
  corresponding 
  median 
  ridge 
  in 
  the 
  sinus. 
  

  

  The 
  lamellose 
  species 
  are 
  conveniently 
  subdivided 
  into 
  two 
  

   groups 
  : 
  

  

  1. 
  Septati 
  ; 
  those 
  having 
  a 
  median 
  septum 
  in 
  the 
  pedicle- 
  

   valve. 
  The 
  septum 
  lies 
  between 
  the 
  bases 
  of 
  the 
  teeth, 
  but 
  does 
  

   not 
  come 
  into 
  contact 
  with 
  them 
  as 
  in 
  the 
  genus 
  Cyetina, 
  where 
  

   the 
  latter 
  are 
  supported 
  by 
  dental 
  lamellae 
  resting 
  on 
  the 
  bottom 
  

   of 
  the 
  valve. 
  

  

  This 
  character 
  is 
  found 
  in 
  an 
  incipient 
  condition 
  of 
  develop- 
  

   ment 
  in 
  the 
  Niagara 
  species 
  Spirifer 
  sulcatus, 
  Hisinger, 
  and 
  is 
  a 
  

   more 
  conspicuous 
  feature 
  in 
  subsequent 
  forms, 
  S. 
  perlamellosus, 
  

   of 
  the 
  Lower 
  Helderberg, 
  S. 
  raricosta, 
  of 
  the 
  Upper 
  Helderberg, 
  

   S. 
  consobrinus, 
  of 
  the 
  Hamilton 
  group, 
  and 
  S. 
  mesacostalis, 
  of 
  

   the 
  Chemung 
  group. 
  Up 
  to 
  the 
  period 
  of 
  the 
  Upper 
  Devonian, 
  

   at 
  least 
  in 
  American 
  faunas, 
  the 
  existence 
  of 
  this 
  septum 
  in 
  the 
  

   pedicle-valve 
  is 
  not 
  accompanied 
  by 
  a 
  pu 
  notation 
  of 
  the 
  shell- 
  

   tissue 
  nor 
  by 
  the 
  union 
  of 
  the 
  processes 
  on 
  the 
  primary 
  lamellae 
  

   of 
  the 
  spiral 
  arms. 
  

  

  6 
  

  

  