﻿Polyzoa 
  of 
  the 
  St. 
  Lawrence. 
  -129 
  

  

  of 
  a 
  prominent 
  mamillary 
  rising, 
  which 
  extends 
  across 
  the 
  

   front 
  wall 
  from 
  side 
  to 
  side 
  immediately 
  below 
  the 
  orifice. 
  

   In 
  the 
  older 
  cells 
  this 
  is 
  completely 
  enveloped 
  and 
  concealed 
  

   by 
  the 
  growing 
  accumulations 
  of 
  calcareous 
  matter. 
  Lorenz 
  

   has 
  met 
  with 
  specimens 
  in 
  which 
  the 
  condition 
  of 
  the 
  younger 
  

   cells 
  is 
  permanent 
  and 
  the 
  avicularian 
  mamillse 
  are 
  conspicu- 
  

   ous 
  throughout 
  the 
  colony*. 
  So 
  completely 
  is 
  the 
  appear- 
  

   ance 
  changed 
  in 
  this 
  specimen 
  that 
  he 
  was 
  at 
  first 
  disposed 
  to 
  

   refer 
  it 
  to 
  a 
  distinct 
  species. 
  He 
  describes 
  the 
  cell 
  as 
  

   being 
  " 
  von 
  milchweisser 
  Farbe 
  und 
  ziemlich 
  diinnwandig." 
  

   From 
  some 
  cause 
  there 
  had 
  been 
  an 
  arrest 
  of 
  calcification. 
  

  

  In 
  many 
  colonies 
  the 
  avicularia 
  are 
  present 
  in 
  great 
  num- 
  

   bers 
  distributed 
  irregularly 
  over 
  the 
  cells 
  ; 
  sometimes 
  one 
  is 
  

   placed 
  immediately 
  above 
  the 
  orifice, 
  sometimes 
  at 
  the 
  side 
  of 
  

   it 
  or 
  on 
  each 
  side. 
  Frequently 
  these 
  sporadic 
  avicularia 
  are 
  

   borne 
  on 
  a 
  prominent 
  mam 
  ilia. 
  

  

  Range. 
  P. 
  concinna 
  lias 
  a 
  very 
  wide 
  range. 
  Common 
  in 
  the 
  

   Northern 
  and 
  Arctic 
  seas 
  ; 
  Britain 
  ; 
  Mediterranean 
  ; 
  Aus- 
  

   tralia. 
  

  

  Porella 
  acutirostris, 
  Smitt. 
  (PI. 
  XXI. 
  fig. 
  5.) 
  

  

  This 
  well-marked 
  species 
  has 
  been 
  described 
  and 
  figured 
  

   by 
  Smitt 
  ; 
  but 
  as 
  yet, 
  I 
  believe, 
  no 
  diagnosis 
  has 
  appeared 
  in 
  

   English, 
  whilst 
  the 
  figures 
  accompanying 
  the 
  excellent 
  

   account 
  of 
  it 
  which 
  we 
  have 
  from 
  the 
  Swedish 
  author 
  are 
  too 
  

   small 
  to 
  be 
  quite 
  satisfactory 
  f. 
  

  

  Zocecia 
  somewhat 
  elongate-oval, 
  distinct, 
  convex, 
  disposed 
  

   in 
  regular 
  lines 
  ; 
  surface 
  minutely 
  granular, 
  of 
  a 
  whitish 
  

   colour 
  ; 
  orifice 
  much 
  broader 
  than 
  high, 
  arched 
  above, 
  lower 
  

   margin 
  straightish, 
  slightly 
  curved 
  inward 
  in 
  the 
  centre; 
  

   peristome 
  not 
  elevated 
  (except 
  in 
  the 
  fertile 
  cells) 
  ; 
  immedi- 
  

   ately 
  below 
  the 
  orifice 
  a 
  prominent 
  mamillary 
  rising, 
  extending 
  

   across 
  the 
  cell, 
  bearing 
  a 
  triangular 
  avicularium, 
  the 
  man- 
  

   dible 
  directed 
  straight 
  outwards. 
  Ocecium 
  large, 
  prominent, 
  

   globose, 
  with 
  a 
  granular 
  surface 
  ; 
  a 
  projecting 
  border 
  above 
  the 
  

   oral 
  arch 
  which 
  meets 
  the 
  elevated 
  peristome 
  at 
  each 
  side. 
  

  

  The 
  zocecia 
  in 
  this 
  species 
  are 
  larger 
  than 
  those 
  of 
  its 
  con- 
  

   gener 
  P. 
  concinna 
  and 
  more 
  distinct 
  and 
  convex. 
  The 
  avicu- 
  

   larian 
  umbo 
  rises 
  much 
  more 
  abruptly 
  than 
  in 
  P. 
  concinna^ 
  

   and 
  it 
  remains 
  distinct 
  over 
  the 
  whole 
  colony, 
  very 
  slightly 
  

   affected 
  by 
  the 
  calcification 
  in 
  the 
  specimens 
  which 
  I 
  have 
  

  

  * 
  ' 
  Bryozoen 
  von 
  Jan 
  Haven,' 
  /. 
  c. 
  p. 
  8, 
  pi. 
  vii. 
  fig. 
  6. 
  

   t 
  Lorenz 
  (I. 
  e. 
  p. 
  8) 
  has 
  given 
  a 
  brief 
  notice 
  of 
  some 
  of 
  the 
  characters 
  

   of 
  the 
  zooecium. 
  

  

  