Yol.  49.]  FROM  THE  DISTRICT  OF  GrIRVAN,  AYRSHIRE.  301 
forward,  beneath  an  antero-dorsal  swelling  or  pseudo-lobe,  which 
dies  away  anteriorly,  leaving  a  narrow,  triangular,  flattened  area  at 
the  front  angle.  The  valve  is  straight  above,  boldly  curved  below, 
and  nearly  semicircular,  with  a  full  postero-ventral  curvature  and 
general  ventral  convexity. 
Mr.  E.  0.  Ulrich  has  a  somewhat  allied  form  (P.  rudis),1  from  the 
Lower-Silurian  (Cincinnati)  group  in  Kentucky ;  but  its  nearly  oblong 
shape,  parallel-sided  sulcus,  and  minute  anterior  tubercle  separate  it 
from  our  fig.  1.  Another  close  ally  is  P.  mundula ,  var.  incisa ,  Jones,2 
from  the  Trenton  Limestone. 
The  boldly  curved  and  expanded  sulcus  of  fig.  1  particularly 
distinguishes  it ;  and  I  propose  to  name  it  Ulrichianci  after  Mr.  E. 
0.  Ulrich,  one  of  our  colleagues  in  the  study  of  Palaeozoic  Ostracoda. 
In  no.  116,  grey  shale. 
Beyrichia  comma ,  Jones,  Monogr.  Girvan  Eoss.  1880,  p.  219, 
pi.  xv.  fig.  9,  may  have  been  a  Primitia  with  a  strong  curved  sulcus 
(and  in  so  far  agreeing  with  fig.  1),  but  with  the  convexity  of  the 
valve  represented  by  a  narrow,  comma-shaped  swelling  bordering  the 
under  side  of  the  sulcus. 
III.  Genus  Beyrichia,  M‘Coy,  1846. 
1.  Beyrichia  Klcedeni,  M‘Coy,  Monogr.  Girvan  Eoss.  Xicholson 
A  Etheridge,  Jun.  vol.  i.  1880,  p.  218,  pi.  xv.  figs.  8  a,  8  b. 
Casts  of  smooth  individuals  from  Thrave  Glen  (Mrs.  Gray’s 
collection),  and  from  Hillside,  near  Blair  Earm,  arfl  Knockgardner 
(Coll.  Geol.  Survey  Scotland),  are  here  referred  to.  A  cast  of  B. 
Klcedeni ,  very  similar  to  that  from  Thrave  Glen,  but  with  evidence 
of  a  tubercuJate  valve,  is  among  the  fossils  from  AYhitehouse  Bay. 
In  no.  116,  grey  shale. 
2.  Beyrichia  Klcedeni,  M‘Coy,  var.  infecta,  nov.  (PI.  XIY. 
fig.  2.) 
Size. — Length  1*24,  height  ’68  millim. 
PI.  XIY.  fig.  2  is  removed  from  PI.  XIII.  fig.  13,  the  lobe  being 
made  more  distinct  by  the  development  of  its  front  curve,  emphasized 
by  an  anterior  notch,  which  indicates  a  real  Beyrichian  character. 
These  features  are  seen  in  a  sharper  and  stricter  form  in  B.  areuata, 
fig.  7  a,  pi.  xvii.  1889,  Ann.  Mag.  Xat.  Hist.,  and  a  much  weaker 
stage  in  Primitia  girvanensis ,  supra,  p.  298. 
Eig  2  is  sufficiently  distinguishable,  with  its  high-placed  forward 
lobe  and  scaphoid  outline,  to  be  regarded  as  a  noticeable  variety, 
infecta ,3  of  B.  Klcedeni. 
There  are  close  links  between  Primitice  with  thickened  sulcus-walls 
and  those  that,  having  one  of  those  edges  swollen  into  a  distinct 
tubercle,  pass  into  a  weak  form  of  Beyrichia.  This  is  traceable 
1  Journ.  Cinciun.  Soc.  Nat.  Hist.  vol.  xiii.  pt.  i.  1890,  p.  136,  pi.  x.  fig.  8. 
2  Geol.  Surv.  Canada,  ‘  Contributions,  etc.,’  pt.  iii.  1891,  p.  64,  pi.  x.  fig.  9. 
3  ‘  Unfinished  ’ :  in  allusion  to  this  form  being  an  imperfect  evolution  of  the 
genus. 
