﻿908 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  ISOTRYPA, 
  Hall. 
  

  

  (Report 
  of 
  the 
  State 
  Geologist 
  of 
  New 
  York, 
  1884, 
  extract. 
  ExpL 
  

   pi. 
  2, 
  figs. 
  13-16, 
  1885. 
  See 
  Pal. 
  K 
  Y., 
  vol. 
  YI, 
  pi. 
  liv, 
  figs. 
  10-21.) 
  

   This 
  genus 
  has 
  some 
  resemblance 
  to 
  Unitrypa, 
  but 
  in 
  reality 
  it 
  

   is 
  very 
  different. 
  In 
  Unitrypa 
  the 
  carinse 
  are 
  very 
  prominent, 
  

   and 
  the 
  scalae 
  or 
  connecting 
  processes 
  are 
  usually 
  thin 
  plates, 
  

   nearly 
  always 
  extending 
  one-half 
  and 
  frequently 
  three-fourths 
  

   the 
  height 
  of 
  the 
  carina, 
  always 
  oblique 
  to 
  the 
  plane 
  of 
  the 
  

   branch, 
  generally 
  sharply 
  bent 
  at 
  about 
  one-half 
  their 
  height, 
  

   and, 
  looked 
  upon 
  from 
  above, 
  always 
  presenting 
  an 
  imbricated 
  

   appearance, 
  frequently, 
  but 
  by 
  no 
  means 
  invariably, 
  correspond- 
  

   ing 
  in 
  number 
  to 
  the 
  cell 
  apertures. 
  The 
  carina 
  is 
  a 
  continuous 
  

   plane 
  of 
  equal 
  strength. 
  

  

  In 
  Isotrypa 
  the 
  connecting 
  processes 
  are 
  round 
  bars. 
  The 
  

   carina 
  is 
  not 
  a 
  continuous 
  plane 
  of 
  equal 
  strength, 
  but 
  is 
  

   much 
  thickened 
  between 
  the 
  cell 
  apertures 
  upwards, 
  so 
  that 
  it 
  

   has, 
  in 
  a 
  slight 
  degree, 
  the 
  appearance 
  of 
  a 
  series 
  of 
  pillars 
  sup- 
  

   porting 
  a 
  crest. 
  When 
  the 
  carina 
  is 
  broken 
  away 
  the 
  remains 
  

   of 
  the 
  thickened 
  portion 
  are 
  much 
  more 
  prominent 
  than 
  of 
  the 
  

   thin 
  portion 
  between, 
  and 
  appear 
  on 
  the 
  branches 
  as 
  a 
  median 
  

   row 
  of 
  semi-circular 
  nodes. 
  On 
  the 
  carina, 
  just 
  above 
  the 
  

   posterior 
  half 
  of 
  each 
  cell 
  aperture, 
  is 
  a 
  circular 
  indentation. 
  

   They 
  may 
  possibly 
  be 
  pores 
  opening 
  into 
  the 
  carina, 
  but 
  none 
  of 
  

   the 
  specimens 
  that 
  I 
  have 
  examined 
  have 
  been 
  in 
  -a 
  condition 
  to 
  

   prove 
  this. 
  On 
  the 
  carina, 
  immediately 
  below 
  the 
  expanded 
  

   69 
  summit 
  and 
  between 
  each 
  two 
  

  

  adjacent 
  thickened 
  portions 
  of 
  the 
  

   carina, 
  are 
  two 
  circular 
  indenta- 
  

   tions, 
  the 
  space 
  between 
  them 
  

   being 
  elevated 
  into 
  a 
  short, 
  rather 
  

   prominent 
  triangular 
  ridge, 
  this 
  

   riangular 
  elevation 
  being, 
  of 
  course, 
  midway 
  between 
  the 
  thick- 
  

   ened 
  portions 
  of 
  the 
  carina 
  (fig. 
  59.) 
  

  

  The 
  expanded 
  summit 
  o£,j 
  the 
  carina 
  v 
  and 
  the 
  connecting 
  

   processes 
  have 
  very 
  much 
  the 
  -appearance 
  of 
  the 
  non-celluliferous 
  

   face 
  of 
  a 
  Fenestella. 
  The 
  characteristic 
  feature 
  of 
  the 
  non- 
  

   celluliferous 
  face 
  is 
  the 
  large 
  apertures 
  or 
  pores 
  situated 
  on 
  or 
  

   near 
  the 
  dissepiments. 
  

  

  