﻿786 
  rBOCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM. 
  volxx. 
  

  

  rounded, 
  obtuse, 
  often 
  prominent 
  lines 
  of 
  growth 
  with 
  a 
  thin 
  yellowish 
  

   brown 
  epidermis 
  which, 
  under 
  the 
  lens, 
  is 
  closely 
  covered 
  with 
  minute 
  

   granules 
  often 
  arranged 
  in 
  more 
  or 
  less 
  distinct 
  concentric 
  lines. 
  The 
  

   posterior 
  hinge-margin 
  is 
  somewhat 
  thickened, 
  the 
  ligamental 
  groove 
  

   is 
  long 
  and 
  curved, 
  diverging 
  considerably 
  from 
  the 
  margin 
  of 
  the 
  

   shell 
  at 
  its 
  posterior 
  end 
  and 
  extending 
  forward 
  under 
  the 
  beak. 
  Mus- 
  

   cular 
  scars 
  and 
  pallial 
  line 
  in 
  the 
  largest 
  specimens 
  strongly 
  marked 
  ; 
  the 
  

   anterior 
  scar 
  is 
  considerably 
  elongated 
  and 
  has 
  a 
  number 
  of 
  lobes 
  or 
  

   scallops 
  on 
  its 
  inner 
  margin. 
  

  

  Length 
  of 
  a 
  medium-sized 
  specimen, 
  27 
  mm.; 
  height 
  from 
  siphonal 
  

   lobe 
  to 
  beak, 
  27 
  mm. 
  ; 
  breadth, 
  14 
  mm. 
  Length 
  of 
  a 
  larger, 
  more 
  ovate 
  

   specimen, 
  32 
  mm. 
  ; 
  height 
  from 
  siphonal 
  lobe 
  to 
  beak, 
  35 
  mm. 
  ; 
  breadth, 
  

   21 
  mm. 
  

  

  This 
  species 
  presents 
  considerable 
  variation 
  in 
  outline 
  and 
  in 
  the 
  

   degree 
  of 
  convexity 
  of 
  the 
  valves; 
  some 
  are 
  subquadrate 
  in 
  form, 
  

   others 
  subcordate, 
  and 
  others 
  pretty 
  well 
  rounded, 
  but 
  the 
  majority 
  

   are 
  oblong-obvate 
  with 
  a 
  posterior 
  truncation, 
  corresponding 
  to 
  the 
  

   broad 
  radial 
  groove; 
  some 
  of 
  the 
  valves 
  are 
  considerably 
  inflated, 
  but 
  

   most 
  of 
  them 
  are 
  more 
  compressed 
  than 
  is 
  usual 
  in 
  this 
  genus. 
  There 
  

   is 
  also 
  considerable 
  variation 
  in 
  the 
  prominence 
  of 
  the 
  siphonal 
  lobe 
  

   and 
  broad 
  radial 
  ridge, 
  and 
  in 
  the 
  size 
  of 
  the 
  lines 
  of 
  growth, 
  which 
  in 
  

   some 
  specimens 
  are 
  quite 
  fine 
  and 
  regular, 
  and 
  in 
  others 
  unevenly 
  

   developed, 
  those 
  on 
  the 
  anterior 
  part 
  appearing 
  almost 
  like 
  concentric 
  

   ribs. 
  

  

  Many 
  separate 
  valves, 
  at 
  four 
  stations 
  between 
  ]^. 
  lat. 
  44° 
  54', 
  W. 
  

   long. 
  59° 
  40' 
  45", 
  and 
  E". 
  lat. 
  42° 
  19', 
  W. 
  long. 
  69° 
  47^', 
  in 
  65 
  to 
  471 
  

   fathoms, 
  1879 
  and 
  1885. 
  

  

  The 
  single 
  valve 
  found 
  off 
  Cape 
  Cod, 
  1879, 
  and 
  identified 
  as 
  Gryp- 
  

   todon 
  sarsii, 
  proves 
  to 
  be 
  the 
  young 
  of 
  this 
  species. 
  

  

  CRYPTODON 
  PLICATUS 
  Verrill, 
  

   (Plate 
  LXXXIX, 
  fig. 
  6.) 
  

   Cryptodon 
  plicattis 
  Verrill, 
  Trans. 
  Conn. 
  Acad., 
  VI, 
  pp. 
  437, 
  450, 
  1885. 
  

  

  One 
  young 
  live 
  specimen 
  and 
  one 
  imperfect 
  valve 
  of 
  this 
  character- 
  

   istic 
  and 
  fragile 
  species 
  were 
  found 
  at 
  two 
  stations, 
  ofi' 
  Marthas 
  Vine- 
  

   yard, 
  in 
  1,073 
  to 
  1,122 
  fathoms, 
  1884. 
  

  

  CRYPTODON 
  CROULINENSIS 
  (Jeffreys) 
  Smith. 
  

   (Plate 
  XC, 
  figs. 
  3, 
  4.) 
  

  

  Clausina 
  croulinensis 
  Jeffreys, 
  Ann. 
  Mag. 
  Nat. 
  Hist., 
  XX, 
  p. 
  19, 
  1847. 
  

  

  Axiniis 
  croulinensis 
  Jeffreys, 
  Brit. 
  Con., 
  II, 
  p. 
  250, 
  1864.— 
  G. 
  O. 
  Sars, 
  Mollusca 
  

  

  Eeg. 
  Arctica) 
  Norvegise, 
  p. 
  62, 
  pi. 
  19, 
  figs. 
  8, 
  a-b, 
  1878.— 
  Jeffreys, 
  Proc. 
  Zool. 
  

  

  Soc, 
  London, 
  p. 
  703, 
  June, 
  1881. 
  

   Cryptodon 
  crouUnensis 
  Smith, 
  E. 
  A., 
  Report 
  Yoy. 
  Challenger, 
  Zool. 
  Lamelli- 
  

  

  hranchiata, 
  XIII, 
  p. 
  193, 
  1885. 
  

  

  Shell 
  small, 
  obhquely 
  subovate, 
  with 
  the 
  beaks 
  prominent, 
  and 
  the 
  

   lanterior 
  end 
  considerably 
  the 
  longer. 
  The 
  antero-dorsal 
  margin 
  is 
  

  

  