﻿No.li;!9. 
  DEEP-WATER 
  MOLLUSC 
  A— 
  VERRILL 
  AND 
  BUSH. 
  829 
  

  

  LYROPECTEN 
  Conrad, 
  1867. 
  

  

  Liropccleii 
  of 
  scvcu'al 
  later 
  authors. 
  

  

  Lyropecten 
  Conrad, 
  1867. 
  — 
  Yekrill, 
  Trans. 
  Con 
  a. 
  Acad., 
  X, 
  pp. 
  (58, 
  89,91, 
  1897 
  

  

  Type. 
  — 
  Lyropecten 
  nodosns 
  (Liiiiia'us). 
  

  

  Shell 
  large 
  and 
  strong, 
  corrugated, 
  with 
  large, 
  fluted, 
  and 
  usually 
  

   nodose, 
  inimary 
  radial 
  ribs, 
  which 
  do 
  not 
  increase 
  in 
  number, 
  and 
  

   with 
  coarsely 
  scallojied 
  margins. 
  Valves 
  somewhat 
  unequal. 
  Auri 
  

   cles 
  of 
  medium 
  size, 
  unequal. 
  Hinge-plate 
  with 
  several, 
  usually 
  three, 
  

   obli(|ue, 
  divergent 
  ribs 
  on 
  each 
  end. 
  This 
  is 
  one 
  of 
  the 
  best 
  defined 
  

   groups, 
  and 
  may 
  bo 
  regarded 
  as 
  of 
  generic 
  value. 
  It 
  is 
  allied 
  to 
  

   PaUium. 
  

  

  PROPEAMUSIUM 
  Gregorio, 
  188S. 
  

  

  I'ropcamiin'unn 
  (subgenus) 
  Dall, 
  Bull. 
  Mus. 
  Conip. 
  Zool., 
  XII, 
  p. 
  210, 
  1886.— 
  

   FiscHEK, 
  18.S7.— 
  (genus) 
  Veurill, 
  Trans. 
  Conn. 
  Acad., 
  X, 
  pp. 
  64, 
  90, 
  92, 
  pi. 
  

   XX, 
  figs. 
  5-9, 
  1897. 
  

  

  Type. 
  — 
  Propeamusmm 
  inequisciilpta 
  (Tiberi) 
  = 
  Fropeamusium 
  fenes- 
  

   Iratnm 
  (Forbes). 
  

  

  This 
  group 
  is 
  allied 
  to 
  Amtmum. 
  It 
  includes 
  small, 
  mostly 
  deep-sea 
  

   species, 
  with 
  thin, 
  rounded 
  shells, 
  having 
  the 
  valves 
  unequal 
  in 
  size 
  

   and 
  sculpture; 
  the 
  lower 
  and 
  flatter 
  one 
  is 
  concentrically 
  grooved, 
  and 
  

   usually 
  turns 
  up 
  at 
  the 
  thin 
  margin 
  to 
  meet 
  the 
  upi)er 
  valve, 
  as 
  in 
  Gyclo- 
  

   pccten. 
  The 
  upper 
  valve 
  may 
  be 
  cancellated 
  or 
  radially 
  sculj^tured. 
  

   When 
  full 
  grown 
  there 
  are 
  several 
  well-formed, 
  raised, 
  internal 
  ribs; 
  

   these 
  may 
  be 
  absent 
  in 
  the 
  young. 
  

  

  This 
  division 
  differs 
  from 
  Amushim 
  in 
  the 
  sculpture 
  of 
  the 
  valves 
  and 
  

   in 
  having 
  the 
  auricles 
  and 
  byssal 
  notch 
  well 
  developed. 
  

  

  The 
  species 
  closely 
  resemble 
  those 
  of 
  Cyelopecten 
  ; 
  the 
  only 
  obvious 
  

   difference 
  in 
  the 
  shells 
  is 
  in 
  the 
  presence 
  of 
  internal 
  ribs. 
  

  

  PALLIOLUM 
  Monterosato, 
  1884. 
  

  

  raUioIuin 
  (subgenus 
  or 
  section) 
  N'ekkill, 
  Trans. 
  Conn. 
  Acad., 
  X, 
  pp. 
  65,90,91, 
  

   pi. 
  xviii, 
  figs. 
  6-M, 
  1897. 
  

  

  Types 
  cited.— 
  Palliolum 
  testie 
  (Bivona) 
  and 
  PalUolum 
  vitreum 
  (Chem- 
  

   nitz). 
  

  

  This 
  grou]) 
  is 
  sepai'ated 
  from 
  Pseudaniiismm 
  H. 
  and 
  A. 
  Adams, 
  and 
  

   can 
  scarcely 
  be 
  distinguished 
  from 
  Gumptonectes 
  by 
  any 
  known 
  char- 
  

   acters. 
  

  

  The 
  two 
  species 
  named 
  by 
  its 
  author 
  as 
  types 
  agree 
  in 
  having 
  thin, 
  

   rounded, 
  nearly 
  equivalved 
  shells, 
  with 
  the 
  posterior 
  auricle 
  poorly 
  

   developed, 
  and 
  with 
  tine 
  camptonectes 
  sculpture 
  on 
  both 
  valves, 
  with 
  

   small 
  radial 
  riblets, 
  and 
  usually 
  with 
  rows 
  of 
  small 
  scales. 
  The 
  mar- 
  

   gins 
  are 
  plain 
  and 
  come 
  evenly 
  together, 
  without 
  flattening. 
  

  

  