﻿364 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  loa 
  

  

  Heck's 
  Iconographic 
  Encyclopaedia 
  (1851, 
  p. 
  84), 
  has 
  given 
  a 
  general 
  

   description 
  of 
  the 
  animal 
  of 
  lo 
  : 
  

  

  Its 
  characters 
  and 
  habits 
  are 
  not 
  those 
  of 
  Fusus, 
  but 
  of 
  [Oxytrema] 
  proper, 
  as 
  

   distinguished 
  from 
  Leptoxis; 
  for 
  although 
  it 
  inhabits 
  the 
  rapids 
  as 
  well 
  as 
  quiet 
  

   water, 
  in 
  both 
  cases 
  it 
  avoids 
  the 
  current 
  by 
  seeking 
  shelter 
  beneath 
  shelving 
  

   rocks, 
  or 
  in 
  hollows 
  or 
  crevices 
  in 
  them. 
  The 
  head 
  is 
  large, 
  and 
  with 
  the 
  tentacles 
  

   much 
  exposed; 
  the 
  foot 
  is^as 
  large^as 
  inr 
  [Oxyirema]; 
  the 
  -coloration 
  is 
  the 
  same 
  

   (black 
  lines 
  upon 
  an 
  orange 
  ground) 
  ; 
  the 
  operculum 
  is 
  subspiral 
  as 
  in 
  [Oxytrema], 
  

   the 
  mantle 
  extends 
  into 
  the 
  canal 
  of 
  the 
  shell, 
  but 
  does 
  not 
  form 
  a 
  closed 
  siphon; 
  

   the 
  vent 
  is 
  upon 
  the 
  right 
  side; 
  the 
  mouth 
  is 
  a 
  longitudinal 
  slit; 
  the 
  eyes 
  (which 
  

   are 
  sensitive 
  to 
  the 
  light) 
  are 
  upon 
  a 
  short 
  enlargement 
  of 
  the 
  outer 
  base 
  of 
  the 
  

   tentacles, 
  which 
  may 
  be 
  a 
  little 
  longer 
  than 
  in 
  [Oxytrema], 
  and 
  they 
  are 
  not 
  visibly 
  

   annulated. 
  It 
  differs 
  from 
  Fusus, 
  and 
  resembles 
  [Oxytrema] 
  in 
  living 
  upon 
  vege- 
  

   table 
  food; 
  and 
  it 
  moves 
  along 
  in 
  a 
  sluggish 
  manner, 
  moving 
  the 
  head 
  from 
  side 
  

   to 
  side 
  upon 
  the 
  bottom. 
  lo 
  spinosa 
  and 
  I. 
  tenebrosa 
  are 
  merely 
  varieties 
  of 
  /. 
  

   fluvialis. 
  The 
  spinose 
  individuals 
  are 
  much 
  the 
  most 
  abundant, 
  although 
  the 
  

   species 
  is 
  rare 
  when 
  compared 
  with 
  various 
  species 
  of 
  [Oxytrema]. 
  

  

  We 
  have 
  taken 
  the 
  liberty 
  of 
  replacing 
  the 
  name 
  "Melania" 
  in 
  the 
  

   foregoing 
  quotation 
  with 
  that 
  of 
  Oxytrema, 
  since 
  Haldeman 
  had 
  

   studied 
  and 
  published 
  as 
  typical 
  of 
  "Melania" 
  the 
  animal 
  of 
  Oxytrema 
  

   virginica 
  (Gmelin) 
  (Haldeman, 
  1841b, 
  p. 
  21). 
  

  

  In 
  this 
  connection, 
  it 
  must 
  be 
  mentioned 
  that 
  the 
  shells 
  of 
  the 
  group 
  

   of 
  " 
  Pleurocera" 
  alveare 
  Conrad 
  (1834, 
  p. 
  54, 
  pi. 
  4, 
  fig. 
  7) 
  look 
  sus- 
  

   piciously 
  like 
  normal 
  sized 
  representatives 
  west 
  of 
  and 
  downstream 
  

   from 
  the 
  megasomatic 
  lo, 
  sensu 
  stricto, 
  species. 
  The 
  generic 
  name 
  

   Megara 
  H. 
  and 
  A. 
  Adams 
  (1854, 
  p. 
  306) 
  has 
  not 
  hitherto 
  been 
  geno- 
  

   typed. 
  Walker 
  (in 
  litt.), 
  quoted 
  by 
  Goodrich 
  (1928, 
  p. 
  2, 
  footnote 
  5), 
  

   incorrectly 
  reported 
  that 
  Hannibal 
  (1912, 
  pp. 
  169, 
  179) 
  had 
  designated 
  

   the 
  type 
  of 
  Megara. 
  Reference 
  to 
  these 
  pages 
  shows 
  that 
  Hannibal 
  

   listed 
  parts 
  of 
  the 
  original 
  Megara 
  twice, 
  with 
  two 
  different 
  species 
  as 
  

   examples 
  (not 
  as 
  types) 
  in 
  the 
  two 
  synonymy 
  lists 
  10 
  pages 
  apart. 
  

   The 
  genotype 
  here 
  designated 
  is 
  the 
  first 
  species, 
  Megara 
  alveare 
  

   (Conrad) 
  1834. 
  Animal 
  characters 
  of 
  this 
  group 
  remain 
  a 
  desideratum. 
  

   If 
  the 
  group 
  is 
  most 
  closely 
  related 
  to 
  Oxytrema, 
  as 
  it 
  has 
  usually 
  been 
  

   regarded, 
  Megara 
  will 
  remain 
  as 
  a 
  synonym 
  of 
  Oxytrema. 
  If, 
  however, 
  

   these 
  species 
  should 
  prove 
  upon 
  examination 
  to 
  be 
  closest 
  to 
  lo 
  in 
  

   relationship 
  of 
  animal 
  characters, 
  their 
  group 
  name 
  Megara 
  will 
  be 
  

   available. 
  

  

  Subfamily 
  pleurocerinae 
  (in 
  Central 
  and 
  South 
  America) 
  

  

  Genus 
  Pachychilus 
  Lea, 
  1851 
  

  

  This 
  genus 
  seems 
  to 
  be 
  the 
  ecological 
  replacement 
  of 
  Oxytrema, 
  to 
  

   the 
  southward 
  of 
  the 
  United 
  States. 
  In 
  my 
  opinion, 
  all 
  the 
  known 
  

   species 
  of 
  this 
  family 
  and 
  subfamily 
  from 
  Central 
  America 
  and 
  the 
  

   West 
  Indies 
  belong 
  to 
  Pachychilus. 
  In 
  this 
  connection, 
  the 
  ichthyol- 
  

  

  