53 
Without  denying  that  this  species  may  have 
been  collected  before,  I  do  not  think  that  it 
has  been  well  defined,  which  obliges  me  to 
give  it  a  name.  I  call  it  centimetralis  to  in¬ 
dicate  the  size  which,  in  this  case,  helps  very 
much  to  recognize  it. 
The  shell  of  centimetralis  has  only  four 
complete  whorls,  or  4  V2,  if  the  hollow  cen¬ 
tre  is  reckoned  as  half  a  whorl.  Their  cali¬ 
bre  increases  rapidly  and  the  end  of  the  last 
whorl  is  bent  (see  Píate  XVII)  upwards 
and  dilated  at  the  mouth.  Form  and  direc¬ 
tion  of  the  whorls,  (fig.  8  b,)  are  so¬ 
mewhat  variable  ;  both  surfaces  are  umbi- 
licated,  the  upper  one  being  more  excavated 
than  the  under  one,  which  may  be  flat  outside 
the  navel.  The  shell  shows  fine  spiral  stria- 
ton  and  an  ocraceus  or,  more  commonly, 
rusty  brown  colour,  being  usually  covered 
with  opaque  scars  and  often  with  algae  and 
other  organisms,  which  may  form  larger 
crusts. 
The  animal  is  black,  but  the  pigment, 
although  generally  abundant,  is  absent  in 
some  animals,  which  show  a  ferrugineus  or 
orange  colour,  partly  due  to  a  large  quanti¬ 
ty  of  red  blood. 
This  species  is  found  m  smaller  and 
larger  brooks,  which  may  even  have  a  swift 
current;  but  then  it  seeks  the  muddy  river-side 
where  the  water  is  more  quiet.  It  feeds 
mainly  on  this  mud  and  does  not  seem  to 
do  well  in  quite  limpid  water. 
The  specimens  found  in  ponds  often 
seem  smaller  and  thicker  and  altogether  a 
little  different,  but  the  dimensions  are  appro¬ 
ximate  and,  there  are  intermediary  forms 
which  do  not  allow  the  distinction  of  two 
species. 
The  largest  diameter  of  the  shell  is  about 
1  cm.,  varying  1  mm.,  to  more  or  less  (1). 
Centimetralis  seems  wanting  in  the  Ca¬ 
pital  of  Pernambuco  and  in  the  river  Bebe- 
ribe,  but  occurs  already  in  Socorro  and  Ja- 
boatão.  It  is  common  in  the  rivers  Capibari- 
1)  The  dimension*  given  by  V.  MARTENS  for 
stramineus  agree  with  our  species  but  not  with  the  ori¬ 
ginal  description. 
be,  Ipojuca,  Una  and  their  affluents,  as  well 
as  in  independent  water-collections  of  the 
same  regions.  It  occurs  also  in  Alagoas  and 
even  to  the  south  of  the  river  S.  Francisco. 
More  to  the  south  I  found  only  a  few  speci¬ 
mens  in  a  brook  near  Retiro,  a  railway-sta¬ 
tion  near  Juiz  de  Fora.  In  Paraguay  I 
found  a  species  very  much  like  it,  if  not  the 
same.  To  the  North  of  Pernambuco  it 
occurs  in  several  natural  ponds,  but  is  wan¬ 
ting  in  a  larger  number.  I  obtained  speci¬ 
mens  in  Independencia  and  in  the  city  of 
Parahyba,  also  from  the  lake  of  Estremoz  and 
a  large  pool  in  Ceará-Mirim  (Rio  Grande 
do  Norte).  I  also  received  specimens  from 
Ceará  and  Maranhão. 
6.  Planorbis  (Taphius)  nigrilabris. 
(Plate  XVI,  Fig.  6  a,  c,  d.) 
This  is  a  small  species,  apparently  not 
described,  which  I  know  only  from  one  place 
near  Rio  de  Janeiro.  This  is  a  pool  full  of 
dead  leaves  and  branches  and  subject  to 
drying  up,  near  kilometer  22  of  the  Leopol¬ 
dina  Railway,  where  it  coexists  with  Planor¬ 
bis  melleus  mihi.  By  its  very  characteristic 
aspect  it  seems  to  belong  to  the  subgenus 
Taphius. 
There  are  four  complete  whorls,  not 
counting  the  hollow  central  part,  or  4  V2  with 
it.  They  have  a  sub-reniform  section,  increa¬ 
sing  rapidly  in  height  and  width.  The  last 
one  is  somewhat  dilated  at  the  mouth  and 
deflected,  in  variable  degree  (upwards  if  the 
shell  be  considered  sinistrai).  The  opening 
becomes  almost  horizontal  ;  it  is  largely  piri¬ 
form,  attaining  2  Va  mm.  in  the  largest  diameter 
which  is  oblique.  The  height  of  this  whorl 
is  not  more  than  1  mm.  The  largest  diameter 
of  the  shell  exceptionaly  attains  6  ram.,  be¬ 
ing  generally  only  5  and  5  Vj. 
The  shell  is  almost  equally  excavated 
on  both  sides  or  a  little  flatter  on  the 
under  side.  It  is  ambercoloured  or,  but  rarely, 
rusty,  with  fine  oblique  striae.  In  mature 
specimens  the  rim  of  the  mouth  is  somewhat 
thickened,  showing  mostly  a  black  border. 
The  animal  is  black  and  through  the  tranepa- 
fent  shell  it  shows  irregular  spot*  of  black  pig- 
