[    335  ] 
XXXVni.  Observations  on  the  Genus  Cancer  of  Dr.  Leach  (Platycarcinus,  Latr.,),  with 
Descriptions  of  three  new  Species.  jB?/ Thomas  Bell,  Esq.,  F.R.S.,  L.S.,  G.8.,  Z.S. 
Communicated  June  9,  1835. 
In  the  course  of  the  gradual  distribution  into  various  genera  of  a  group  of  animals 
previously  arranged  under  a  single  generic  term,  it  is  not  always  a  matter  devoid  of 
difficulty  to  decide  by  which  of  the  newly  distinguished  groups  that  original  appellation 
should  be  retained ;  and  different  rules  have  been  laid  down,  and  different  principles 
resorted  to,  by  various  naturalists  on  this  point,  whilst  others  have  been  wholly  careless 
on  the  subject.  The  consequence  of  this  discrepancy  has  been  the  absence  of  all  unity 
of  design  in  the  present  heterogeneous  nomenclature  of  the  different  divisions  of  the 
animal  kingdom,  according  to  the  varying  views  adopted  by  the  individuals  by  whom 
each  portion  has  been  separately  studied  and  developed. 
It  is  undoubtedly  desirable  where  a  particular  species  can,  with  tolerable  certainty, 
be  recognised  as  having  received  a  distinct  appellation  from  any  of  the  early  masters  of 
natural  science,  to  retain  that  name  for  the  genus  to  which  the  species  belongs,  and 
still  to  consider  it  as  designating  the  smaller  group  in  which  it  is  included,  whatever 
may  be  the  changes  and  subdivisions  made  in  the  larger  group  to  which  it  was  origin- 
ally attached.  This  is  still  more  imperative  when  the  name  has  been  so  applied  by  any 
modern  naturalist,  whose  character  for  learning  and  accuracy  is  such  as  to  give  weight 
to  his  opinion  in  matters  of  nomenclature.  It  appears  to  me  that  the  name  which  I 
propose  to  retain  for  the  genus  which  is  the  subject  of  this  paper  is  thus  strongly  re- 
commended for  our  adoption,  as  being  very  probably  the  one  by  which  the  type  of  that 
genus  was  known  to  the  older  writers,  and  which  has  recently  been  applied  by  one  of 
our  most  distinguished  carcinologists,  to  the  genas  restricted  by  himself  to  the  only 
species  of  it  then  known  to  him.  The  generic  name  Cancer  was  applied  by  Dr.  Leach 
to  the  species  Cane.  Pagurus,  with  the  full  understanding  that  it  constituted  the  type  of 
a  form  distinct  from  all  others  of  the  family.  I  have  therefore  chosen  this  opportu- 
nity to  claim  for  it  the  same  distinction,  upon  the  ground  that  the  group  was  so  desig- 
nated by  my  distinguished  friend,  before  the  term  Platijcarcinus  was  applied  to  it  by 
Latreille  in  the  French  Museum,  and  consecrated  by  Dr.  Milne  Edwards  in  his  recent 
admirable  work  on  the  natural  history  of  Crustacea  ;  and  also  because,  by  applying  any 
other  term  to  this  genus,  we  are  obliged  to  restrict  the  word  Cancer  to  a  small  and  com- 
paratively unimportant  group,  not  a  single  species  of  which  was  probably  distinctly 
known  to  any  naturalist  of  early  times. 
When  the  characters  of  the  present  genus  were  first  defined,  the  only  known  species 
2  Y  2 
