﻿new 
  Shells 
  from 
  British 
  East 
  Africa. 
  475 
  

  

  Opeas 
  avgustior, 
  sp. 
  n. 
  (Fig. 
  33.) 
  

  

  Shell 
  differing 
  from 
  0. 
  rumrutiensis 
  in 
  its 
  rather 
  narrower 
  

   form 
  and 
  more 
  acuminate 
  apex, 
  in 
  having 
  an 
  additional 
  

   whorl 
  and 
  a 
  half, 
  coarser 
  transverse 
  sculpture, 
  crenellate 
  and 
  

   not 
  margined 
  suture, 
  more 
  obliquely 
  descending 
  columella, 
  

   and 
  shorter 
  aperture. 
  

  

  Alt. 
  7*25, 
  diam. 
  maj. 
  nearly 
  2 
  mm. 
  

  

  Aperture 
  : 
  alt. 
  1'25, 
  diam. 
  '5 
  mm. 
  

  

  Hub. 
  Between 
  Rumruti 
  and 
  Mount 
  Kenia, 
  British 
  East 
  

   Africa. 
  

  

  Opeas 
  vicina, 
  sp. 
  n. 
  (Fig. 
  31.) 
  

  

  Shell 
  differing 
  from 
  0. 
  angustior 
  in 
  its 
  shorter 
  and 
  more 
  

   tapering 
  form, 
  rather 
  more 
  convex 
  whorls, 
  of 
  which 
  there 
  are 
  

   but 
  six, 
  coarser 
  sculpture, 
  rather 
  less 
  oblique 
  columella, 
  and 
  

   shorter 
  aperture. 
  

  

  Alt. 
  5'25, 
  diam. 
  maj. 
  1*75, 
  diam. 
  min. 
  1*5 
  mm. 
  

  

  Aperture 
  : 
  alt. 
  1, 
  diam. 
  *5 
  mm. 
  

  

  Hab 
  Between 
  Rumruti 
  and 
  Mount 
  Kenia, 
  British 
  East 
  

   Africa. 
  

  

  Ancylus 
  crassistriatus, 
  sp. 
  n. 
  (Fig. 
  35.) 
  

  

  Shell 
  somewhat 
  conical, 
  oval, 
  with 
  subcentral 
  apex, 
  choco- 
  

   late-brown 
  in 
  colour, 
  sculptured 
  with 
  coarse, 
  wavy, 
  radiate 
  

   strise 
  ; 
  margin 
  somewhat 
  serrated 
  ; 
  interior 
  reddish 
  brown, 
  

   polished, 
  shining. 
  

  

  Alt. 
  2, 
  diam. 
  maj. 
  4"5, 
  diam. 
  min. 
  3 
  mm. 
  

  

  Hab. 
  Between 
  Rumruti 
  and 
  Mount 
  Kenia, 
  British 
  East 
  

   Africa. 
  

  

  Pisidium 
  kenianum, 
  sp. 
  n. 
  (Fig. 
  36.) 
  

  

  Shell 
  solid, 
  somewhat 
  trigonal, 
  convex, 
  very 
  finely 
  con- 
  

   centrically 
  striate; 
  umbones 
  large; 
  dorsal 
  margin 
  arched; 
  

   ventral 
  margin 
  rounded 
  ; 
  anterior 
  side 
  rather 
  abruptly 
  

   descending; 
  posterior 
  side 
  slightly 
  produced, 
  rounded; 
  

   cardinal 
  teeth 
  in 
  right 
  valve 
  small, 
  oblique 
  ; 
  anterior 
  lateral 
  

   elongate, 
  erect; 
  posterior 
  lateral 
  also 
  elongate, 
  slightly 
  

   rounded; 
  cardinal 
  teeth 
  in 
  left 
  valve 
  situated 
  at 
  an 
  obtuse 
  

   angle 
  to 
  one 
  another, 
  the 
  anterior 
  broad 
  below, 
  the 
  posterior 
  

   small 
  ; 
  the 
  anterior 
  lateral 
  in 
  left 
  valve 
  posteriorly 
  bifid, 
  

   angled 
  in 
  the 
  middle, 
  outwardly 
  projecting; 
  the 
  posterior 
  

   lateral 
  elongately 
  anteriorly 
  bifid, 
  also 
  projecting, 
  slightly 
  

   grooved 
  above. 
  

  

  