49 
black  pigment  and  the  abundant  red  blood 
lends  its  colour  to  the  tissues,  principally  to 
these  of  the  visceral  sack.  The  shell  is  carried 
more  or  less  perpendicular  to  the  support 
and  has  a  corneous  appearance.  In  life  it  is 
transparent,  with  ocraceous  yellow  or  reddish- 
brown  tint.  In  pathological  conditions  and  after 
death  it  becomes  opaque.  All  of  them  have 
at  least  five  whorls  when  adult.  Young  spe¬ 
cimens  already  show  differences  in  the  shell, 
which,  however,  is  less  dark,  almost  vitreous. 
The  tissues  also  are  less  pigmented  and  the 
tegument  of  the  respiratory  cavity  is  only 
spotty  (fig.  6).  The  red  visceral  part  and 
the  position  of  the  shell  show  that  they  are 
young  forms  and  not  a  small  species. 
The  small  species  in  the  second  plate 
(magnified)  carry  the  shell  generally  paral¬ 
lel  to  the  support  and  the  blood  is  often 
apparently  colourless. 
I  begin  with  the  largest  species,  of 
which  theie  are  descriptions  and  drawings 
permitting  to  identify  them. 
1.  Planorbis  olivaceus  SPIX 
(Plate  XV,  fig.  1,  a,  b,  c,  d  ;  XVIII  1,  2). 
Syn.  PI.  cummingianus  (?),  PI.  bahiensis 
DUNKER. 
I  give,  in  plate  I,  good  figures  of  this 
species  which  seems  limited  to  the  North 
of  Brazil;  it  does  not  occur  near  Rio  de  Ja¬ 
neiro  which  is  important,  as  it  is  one  of  the 
principal  intermediate  hosts  of  Schistosomum 
mansoni.  It  is  larger  than  all  the  other  spe¬ 
cies.  Samples  received  in  large  numbers  from 
Aracajú  were  observed  alive  during  a  long 
period  and  agreed  well  with  the  drawings  of 
SPIX  and  one  of  SOWERBY  in  the  Con- 
ehologia  of  REEVE,  also  with  one  PIRAJÁ 
gave  of  PL  bahiensis.  The  large  Planorbis  of 
Bahia  agree  in  every  detail  with  those  of 
Aracajú,  as  I  have  since  observed.  Though 
the  drawings  mostly  represent  the  shell 
only,  they  are  sufficient  because  it  is  well 
characterized.  The  adjective  olivaceus  does 
not  fit  the  shell  very  well,  but,  combined  with 
brown  or  black,  might  refer  to  the  animal 
which  is  less  black  than  in  the  two  next 
species.  The  two  authors,  SPIX  and  WAG¬ 
NER,  consider  the  shell  dextral  and  give 
the  following  description: 
“ Planorbis  oliváceos.  Tab.  XVIII,  Fig.  1. 
PI.  testa  discoidea,  tenui,  superne  piano 
depressa,  inferne  late  umbilicata,  olivácea, 
anfractu  ultimo  compresso. 
a.  Testa  maiore:  PI.  olivaceus  SPIX, 
Tab.  XVIII  fig.  2. 
b.  Testa  minore:  PI.  ferrugineus  SPIX, 
Tab.  XVIII,  fig.  1. 
Testa  discoidea,  tenuis,  oellucida,  oblique 
striata  superne  plano  depressa,  inferne  late 
umbilicata,  epiderme  tenuíssima  vestita.  An- 
fractus  quinqué  plano-convexi  ;  ultimus  ma- 
ximus  versus  peripheriam  compressus;  omnes 
gyri  umbilico  latissime  visibiles.  Apertura 
valvae  obliqua  ;  margine  acuto.  Color  epi¬ 
dermis  olivaceo-viridis  aut  olivaceo-lutescens  ; 
apertura  alba;  color  testae  decorticatae  cae- 
ruleo-albidus.  Lcngitudo  3  Va  lin.,  latitudo  1 
poll.  2  Va  lin. 
Habitat  in  rivulis  silvestribus  ad  Ilheos 
et  Almada,  provincia  bahiensi. 
Observado  :  Differt  haec  species  a  pla- 
norbi  corneo  testa  humiliore,  anfractuque  ul¬ 
timo  compresso/* 
To  judge  by  the  figures  given,  WAGNER 
was  right  in  considering  the  specimen,  named 
ferrugineus  by  SPIX,  as  just  a  small  indivi¬ 
dual  of  olivaceus.  Thus  it  would  be  a  syno¬ 
nym,  as  also  probably  albescens  and  viridis 
which  WAGNER  considered  as  young  spe¬ 
cimens  of  another  species  (Planorbis  lugu- 
bris  WAGNER),  found  in  the  same  place. 
D’ORBIGNY,  who  probably  never  ob¬ 
served  the  real  olivaceus,  referred  to  ferrugi¬ 
neus  a  rather  common  species  of  Rio  de  Ja¬ 
neiro  where  the  real  olivaceus  is  not  found. 
This  same  species,  which  I  shall  call  confu - 
sus,  was  figured  in  the  Conchologia  iconica 
also,  with  the  ame  of  ferrugineus. 
The  exact  drawings  given  in  plate  XV 
make  a  detailed  description  of  the  shell 
superfluous.  I  saw  many  specimens  of  the 
size  represented,  the  largest  diameter  being 
33  to  35  mm.,  but  most  of  the  individuals 
found  are  smaller.  The  height  of  the 
whorls,  with  exception  of  the  last,  is  rather 
constant  and  always  small;  the  last  one 
