56 
MR.  E.  T.  BENNETT  ON  THE  CHINCHILLID^E. 
Distance  between  the  orbits  above'     .  . 
Diastematic  distance,  upper  jaw     ,    .  . 
■  lower  jaw    .    .  . 
Length  of  molar  series  in  each  jaw     .  . 
 mastoid  process,  or  inferior  di- 
vision of  the  tympanic  cells    .    .  . 
Greatest  breadth  of  do  
Length  of  the  lower  jaw  (including  the 
teeth)  
Height  of  the  coronoid  process  .... 
Length  of  the  clavicle  
 1   scapula  
  humerus  
  radius  
  ulna  
 fore-foot  to  the  end  of  the 
middle  finger 
Length  of  the  pelvis  from  the  crista  ilii  to 
the  tuber  ischii  
Greatest  breadth  of  do  
Length  of  the  femur  
  tibia  
 hind-foot  from  the  calca- 
Lagotis. 
In. 
•8 
•9 
•7 
•7 
•6 
•45 
2-5 
•8 
■9 
1-8 
2- 
1-  9 
2-  4 
1-4 
3-3 
1-7 
3- 
3-8 
3-6 
Chinchilla. 
In. 
•45 
•5 
•4 
•5 
•7 
•5 
1-8 
•7 
•6 
1-2 
1-2 
1-2 
1-6 
2-2 
1-2 
1-  9 
2-  3 
2-2 
neum  to  the  end  of  the  longest  toe  . 
With  the  animals  just  described  Lagostomus  corresponds  in  the  general  composition 
of  its  skeleton,  and  even  in  the  form  and  proportion  of  most  of  the  separate  bones.  It 
is  still  larger  in  size  than  Lagotis ;  and  the  figure  accompanying  Mr.  Brookes's  de- 
scription exhibits  several  very  striking  differences  in  the  form  of  the  cranium.  As, 
however,  the  details  of  that  important  part  are  not  there  made  out  with  sufficient  clear- 
ness, and  I  possess  no  notes  relative  to  its  peculiarities,  I  can  do  no  more  than  refer  to 
the  plate  itself.  The  number  of  ribs  on  each  side,  and  consequently  of  the  dorsal  ver- 
tebra, was  twelve,  and  that  of  the  lumbar  vertebra  seven,  corresponding  in  these  par- 
'  This  and  the  zygomatic  breadth  depend  in  Lagotis  on  the  less  oblique  and  more  lateral  position  of  the  eyes, 
the  orbits  of  which  have  their  margins  also  much  expanded,  a  structure  perhaps  connected  with  more  nocturnal 
habits. 
