358 
in  the  middle  of  the  excision  or  else  at  the  base  of  the  anterior  border  of 
the  posterior  tooth.  The  last  two  keels  only  very  obscurely  bidentate. 
Copulatory  foot  different  from  that  of  the  two  preceding  species  in 
that  the  lower  process  is  much  the  shorter  and  thinner  of  the  two 
and  is  curved  backwards  from  its  base,  while  the  superior  process 
is  in  its  distal  half  curled  completely  on  itself. 
Length  about  54  mm.;  width  of  10**  somite  6;  of  1st  5.5,  length 
of  Is*  2.2. 
This  species  may  be  recognised  at  once  from  the  two  preceding 
by  the  difference  in  the  form  of  the  two  teeth  of  the  keels,  the  posi- 
tion of  the  pore  and  the  form  of  the  copulatory  foot. 
Strongylosoma ,  Brandt. 
I  include  under  this  genus  both  Strongylosoma  of  Brandt  and  authors  , 
and  the  species  of  Paradesmus  of  the  gracilis  and  coarctatus  type. 
There  seems  to  be  little  besides  the  size  of  the  keels  to  separate  these 
two  so-called  genera,  but  this  is  obviously  a  character  which  is  sub- 
ject to  a  large  amount  of  specific  variation  within  the  limits  of  the 
same  genüs. 
The  species  discussed  in  this  paper  present  the  following  features 
in  common.  The  segments  are  either  strongly  or  weakly  keeled  and 
the  pores  are  situated  on  the  lateral  margins  of  the  keels  towards 
their  posterior  extremity.  The  Ist  segment  is  scarcely  if  at  all' keeled; 
but  the  keel  of  the  2nd  is  large  and  projects  below  the  level  of  the 
edge  of  the  1st  and'  of  the  keel  of  the  3»d.  The  keel-bearing  part  of 
the  segments  from  the  5th  to  about  the  l8t  is  furnished  with  a  trans- 
verse groove  lying  between  the  bases  of  the  keels;  sometimes  the 
area  is  also  marked  more  or  less  clearly  by  a  longitudinal  groove.  The 
tail  is  truncate  and  bitubercular  apically  and  usually  considerably  bro- 
ader at  the  base  than  at  the  distal  end.  The  anal  sternite  is  trian- 
gular and  bitubercular.  The  sternal  areas  conspicuous,  the  legs  con- 
sequently separated  widely  at  the  base.  The  femur  (3rd)  and  tarsus 
(6th)  segments  of  the  legs  are  the  longest.  Legs  and  antennce  both 
rather  slender.  There  is  frequently  a  crest  above  the  base  of  the  legs , 
especially  in  the  anterior  half  of  the  body. 
The  copulatory  feet  of  the  cT  are  entirely  free  at  the  base,  being 
unprotected  by  upgrowths  of  the  sternal  area  which  supports  them; 
