[    35  ] 
VI.  On  the  Chinchillidse,  a  Family  of  Herbivorous  Rodentia,  and  on  a  new  Genus 
referrible  to  it.    By  E.  T.  Bennett,  Esq.,  F.L.8.,  Sec.  Z.S. 
Communicated  May  14,  1833. 
In  the  well-defined  division  of  the  purely  Herbivorous  Rodentia,  characterized  by  the 
want  of  distinct  roots  to  their  molar  teeth,  which  are  continually  growing  by  the  ad- 
dition of  fresh  matter  to  their  base  as  their  crown  is  worn  away  by  attrition,  the  little 
family  which  I  propose  to  designate  Chinchillida  is  deserving  of  peculiar  attention. 
This  family  (which  may  at  once  be  distinguished  by  its  teeth,  consisting  of  either  two 
or  three  parallel  and  ribband-like  bony  lamella,  eacli  surrounded  by  its  own  proper 
coat  of  enamel,  and  connected  to  its  neighbour  by  the  intervention  of  cortical  substance 
alone,)  consists  at  present  of  two  genera,  both  established  within  the  last  five  years, 
Lagostomus  and  Chinchilla.  Of  the  former,  one  species  only,  the  Viscacha  of  the  plains 
of  Buenos  Ayres,  has  been  described.  Of  the  latter,  besides  the  Chinchilla,  long  popu- 
larly known  for  the  extreme  fineness  and  beauty  of  its  fur,  and  of  late  scientifically  de- 
scribed by  various  writers,  there  appears  to  exist  a  second  species,  the  mutilated  skins 
of  which  have  not  yet  afforded  sufficient  materials  for  its  complete  definition.  To  these 
I  have  now  to  add  a  third  genus,  which  I  have  no  hesitation  in  regarding  as  new  to 
science,  although,  if  my  conjecture  as  to  the  origin  of  the  animal  be  correct,  it  has 
been  repeatedly  noticed  by  travellers  for  a  period  of  nearly  three  hundred  years. 
In  describing,  after  D'Azara,  the  Viscacha  of  the  Pampas  of  Buenos  Ayres  and  Para- 
guay, M.  Desmarest'  refers  to  an  unpublished  drawing  by  Feuillee  of  a  Viscacha  ob- 
served by  that  author  in  Peru,  and  suggests  the  probability  of  its  belonging  to  a  distinct 
species.  A  careful  comparison  of  the  scattered  notices  published  by  travellers  and 
naturalists  of  the  Viscachas  of  the  Eastern  and  Western  sides  of  the  Andes,  had  long 
since  led  me  to  form  a  similar  opinion  as  to  their  distinctness.  This  opinion  was  fully 
confirmed  on  the  acquisition  by  the  Society,  in  the  month  of  June  last,  of  a  living 
animal,  obviously  nearly  allied  to  the  Viscacha  of  Buenos  Ayres,  but  possessing  the 
distinguishing  peculiarities  of  the  Peruvian  species  ;  and  which  consequently,  although 
no  information  could  be  obtained  as  to  its  native  country,  I  did  not  hesitate  to  refer  to 
that  obscure  but  highly  interesting  form.  At  the  next  Meeting  of  the  Committee  of 
Science  and  Correspondence  1  made  some  remarks  on  its  affinities,  pointing  out  various 
external  characters  by  which  it  was  distinguished  from  both  Chinchilla  and  Lagostomus, 
the  only  two  genera  with  which  it  appears  to  come  into  immediate  contact ;  and  inti- 
mated my  intention  of  establishing  on  it,  whenever  its  death  might  furnish  the  oppor- 
*  Mammalogie,  p.  360,  note. 
F  2 
