﻿Report 
  of 
  the 
  State 
  Geologist. 
  891 
  

  

  Many 
  species 
  can 
  be 
  very 
  naturally 
  arranged 
  in 
  groups 
  from 
  

   the 
  character 
  of 
  the 
  separating 
  nodes 
  or 
  carinae. 
  In 
  the 
  sixth 
  

   volume 
  of 
  the 
  Palaeontology 
  of 
  the 
  State 
  of 
  ~New 
  York 
  the 
  Fenes- 
  

   tellidae 
  have 
  been 
  described 
  under 
  four 
  groups 
  as 
  follows 
  : 
  Those, 
  

  

  First, 
  in 
  which 
  the 
  ranges 
  of 
  apertures 
  are 
  separated 
  by 
  a 
  row 
  

   of 
  nodes, 
  or 
  a 
  low 
  carina 
  with 
  a 
  row 
  of 
  nodes 
  on 
  the 
  summit 
  (figs. 
  

   34, 
  35). 
  

  

  Second, 
  in 
  which 
  the 
  ranges 
  of 
  cell 
  apertures 
  are 
  separated 
  by 
  a 
  

   smooth 
  carina. 
  

  

  Third, 
  in 
  which 
  the 
  ranges 
  of 
  apertures 
  are 
  separated 
  by 
  a 
  

   prominent 
  carina, 
  which 
  at 
  about 
  half 
  its 
  height 
  is 
  expanded, 
  

   then 
  contracted, 
  the 
  portion 
  above 
  the 
  expansion 
  being 
  of 
  the 
  

   same 
  thickness 
  as 
  the 
  portion 
  below. 
  On 
  the 
  margin 
  of 
  the 
  

   expanded 
  portion 
  there 
  are 
  usually 
  small 
  conical 
  nodes 
  (figs.36, 
  37). 
  

  

  Fourth, 
  in 
  which 
  the 
  ranges 
  of 
  apertures 
  are 
  separated 
  by 
  

   a 
  prominent 
  carina, 
  expanded 
  at 
  the 
  summit; 
  margins 
  of 
  these 
  

   expanded 
  portions 
  smooth 
  (figs. 
  38-41). 
  

  

  To 
  these, 
  two 
  other 
  groups 
  may 
  be 
  added, 
  one 
  where 
  the 
  carina 
  

   is 
  very 
  prominent, 
  more 
  cr 
  less 
  expanded 
  at 
  the 
  summit 
  and 
  

   with 
  lateral 
  nodes 
  ; 
  the 
  other 
  with 
  a 
  very 
  prominent 
  carina, 
  of 
  

   the 
  same 
  thickness 
  throughout, 
  not 
  expanded 
  either 
  midway 
  of 
  

   their 
  height 
  or 
  at 
  the 
  summit 
  (figs. 
  42, 
  43). 
  

  

  At 
  first 
  thought 
  the 
  character 
  of 
  the 
  carinae 
  may 
  not 
  seem 
  of 
  

   much 
  importance, 
  but 
  when 
  we 
  reflect 
  that 
  several 
  genera 
  are 
  

   founded 
  upon 
  the 
  character 
  of 
  the 
  carinae 
  or 
  structure 
  above 
  the 
  

   celluliferous 
  face 
  of 
  the 
  branches 
  the 
  subject 
  becomes 
  of 
  more 
  

   importance. 
  

  

  The 
  genera 
  Hemitrypa, 
  Unitrypa, 
  Tectuliporella, 
  Tectulipora 
  

   and 
  Loculipora 
  are 
  essentially 
  founded 
  upon 
  the 
  character 
  of 
  the 
  

   carinae, 
  the 
  first 
  four 
  being 
  based 
  upon 
  the 
  character 
  of 
  the 
  

   lateral 
  processes 
  of 
  the 
  carinae 
  and 
  the 
  remaining 
  two 
  chiefly 
  on 
  

   the 
  carinae 
  of 
  the 
  dissepiments. 
  

  

  There 
  can 
  be 
  no 
  arbitrary 
  rule 
  fixing 
  characters 
  of 
  generic 
  

   importance. 
  It 
  has 
  always 
  been 
  the 
  case 
  and 
  will 
  probably 
  

   always 
  continue 
  to 
  be, 
  that 
  what 
  one 
  person 
  considers 
  to 
  be 
  of 
  

   generic 
  importance 
  another 
  will 
  consider 
  to 
  be 
  of 
  only 
  specific 
  

   importance. 
  In 
  fact 
  it 
  seems 
  to 
  be 
  a 
  favorite 
  pastime 
  of 
  some 
  

   writers 
  to 
  destroy 
  the 
  genera 
  of 
  others 
  solely 
  to 
  erect 
  other 
  

   genera 
  from 
  the 
  ruins. 
  

  

  