﻿510 
  

  

  PliOCEEDINGS 
  OF 
  THE 
  XATIOXAL 
  MUSEUM. 
  

  

  the 
  middle 
  of 
  tlie 
  back 
  and 
  disappear 
  altogetlier 
  anteriorly 
  except 
  near 
  

   tlie 
  margins. 
  Head 
  marked 
  off 
  by 
  two 
  deep 
  notches; 
  squarish 
  or 
  

   retuse 
  in 
  front, 
  with 
  suborbicular 
  anterior 
  sneakers 
  on 
  under 
  side. 
  

   Mouth 
  between 
  posterior 
  n)argins 
  of 
  antei-ior 
  suckers, 
  transversely 
  ellip- 
  

   tical, 
  appearing 
  like 
  a 
  transverse 
  slit. 
  Posterior 
  sucker 
  (acetabulum) 
  

   circular, 
  with 
  crenulate 
  or 
  ruffled 
  membranous 
  border, 
  pedicelled, 
  with 
  

   seven, 
  sj'mmetrical 
  rays 
  radiating 
  from 
  a 
  central 
  ring, 
  thus 
  making, 
  

   with 
  the 
  central 
  space, 
  eight 
  locnli. 
  

  

  The 
  marginal 
  papilhe 
  in 
  one 
  specimen 
  were 
  thirty-four 
  in 
  number. 
  

   The 
  lirst 
  papilla, 
  anteriorly, 
  had 
  one 
  granule; 
  the 
  next 
  three 
  pai)illie 
  

   had 
  two 
  grannies 
  each; 
  the 
  following 
  two 
  papilla- 
  had 
  three 
  granules 
  

   each; 
  the 
  following 
  nine 
  papilhv 
  had 
  four 
  granules 
  each; 
  the 
  next 
  

   seventeen 
  papilla^ 
  had 
  three 
  granules 
  each; 
  and 
  the 
  last 
  two 
  papillai 
  

   had 
  two 
  granules 
  each. 
  

  

  Dimensions 
  of 
  two 
  living 
  specimens 
  of 
  Tristonmm 
  coccinenm. 
  

  

  Measuremeuts. 
  

  

  Length 
  

  

  Greatest 
  breadth 
  

  

  Breadth 
  at 
  anterior 
  eud 
  

  

  Breadtli 
  opposite 
  posterior 
  sucker 
  

  

  Diameter 
  of 
  an 
  anterior 
  snrker 
  

  

  Diameter 
  of 
  posterior 
  sucker 
  

  

  Breadth 
  of 
  head, 
  projecting 
  between 
  anterior 
  suckers 
  

  

  5. 
  TRISTOMUM 
  RUDOLPHIANUM 
  Diesing. 
  

  

  Tristomum 
  coccinenm 
  Rudolphi, 
  Dujardin, 
  Hist. 
  Helm., 
  ji. 
  322. 
  

   Tristonmm 
  rndolphiannm 
  Diesing, 
  Syst. 
  Helm., 
  I, 
  p. 
  429. 
  

  

  Body 
  flattened, 
  suborbicular 
  posteriorly 
  emarginate, 
  minutely 
  pit. 
  

   ted 
  beneath. 
  Anterior 
  bothria 
  suborbicular. 
  Acetabulum 
  (posterior 
  

   sucker) 
  with 
  a 
  plicate 
  membranaceous 
  border; 
  length, 
  18 
  to 
  22 
  mm. 
  

  

  On 
  Molamola; 
  Woods 
  Holl, 
  Massachusetts, 
  July 
  13, 
  1881. 
  Nineteen 
  

   specimens. 
  No. 
  4879, 
  U.S.N.M. 
  

  

  Dimensions 
  of 
  two 
  alcoholic 
  specimens 
  of 
  Tristomum 
  rudolphianum. 
  

  

  One 
  specimen 
  was 
  12.5 
  mm. 
  in 
  length 
  and 
  14 
  in 
  breadth; 
  another 
  was 
  

   14.") 
  in 
  length 
  and 
  12.5 
  in 
  breadth. 
  They 
  are 
  mostly 
  orbicular, 
  but 
  the 
  

   ratio 
  of 
  length 
  to 
  breadth 
  varies 
  with 
  the 
  state 
  of 
  contraction. 
  

  

  The 
  specimens 
  agree 
  with 
  the 
  descriptions 
  of 
  this 
  species 
  given 
  bj' 
  

   Diesing 
  and 
  Dujardin. 
  The 
  plicated 
  ruffle 
  like 
  margin 
  of 
  the 
  acetabu- 
  

   lum 
  is 
  ab(»ut 
  1 
  mm. 
  deep. 
  The 
  posterior 
  emargination 
  is 
  as 
  much 
  as 
  

   4.5 
  mm. 
  deep. 
  

  

  