614 
Proceedings of Eoyal Society of Edinburgh. [sess. 
53. 
54. 
55. 
{ 
{ 
{ 
56.- 
Two asymmetrical distant curved depressions 
at border. A rosette, ..... 
No such depressions, 
Border broad, its inner edge with 2 asymmetrical 
constrictions. No rosette, .... 
No such constrictions, 
Largest markings forming a conspicuous, not 
sharply defined zone towards semiradius, 
No such zone, 
Markings towards centre 6 in *01 mm., decreasing 
slightly outwards, secondary rows obscure. 
Border sharp, \ of radius broad, striae evident, 
4 in *01 mm., 
Markings 3i, towards border 2^, in *01 mm. 
Surface with an elevated ring about \ of radius 
from centre, ....... 
Markings 1| to 2, at border 2 to 2|, in *01 mm., 
pearly ; central papillae prominent, directed 
centrally towards border, .... 
Markings 5 to 7 in *01 mm., slightly smaller 
towards centre, papillae evident, minute sub- 
ulate areas at origin of shorter rows. Border 
opaque, . 
Markings increasing gradually outwards, at 
centre 8, at border 6, in *01 mm. ; irregular 
on a small central area, secondary oblique rows 
distinct, ....... 
Markings 2| to 3 in *01 mm., subequal, central 
papillae small. Border broad, 
Markings 6^ to 7 in *01 mm., decreasing rapidly 
outwards, interspaces evident opposite shorter 
rows, . . 
Markings towards centre 4, towards border 6, in 
*01 mm., decrease outwards gradual. A rosette, 
Markings towards centre 6 to 9, near border 9 to 
10, in *01 mm. ; minute subulate lines at origin 
of shorter rows, ...... 
Markings towards centre 4, decreasing outwards 
to 6 or 7, in *01 mm. ; radial rows most evident 
towards border, fimbriate, .... 
Markings towards centre 2 to 2|, at border 8, in 
*01 mm., decrease outwards rapid; radial rows 
separated by distinct lines around border, 
central papillae distinct, .... 
Markings towards centre 2 to 2J, near border 6, 
in *01 mm. Border narrow, .... 
Markings towards centre 2 to 2\, robust. Border 
broad, sharply defined, striae coarse, 
Markings towards centre 1^ to 2J, central papillae 
prominent. Border conspicuous, raised, striae 
coarse, ... .... 
Markings towards centre 3 to 4, increasing to 2\ 
or 3, at border 5 or 6, in *01 mm. Central 
rosette large, 
Markings towards centre 8, at semiradius 4, 
towards border 8, in *01 mm., on outer half of 
valve in inconspicuous, subcon centric bands, . 
Markings at centre large, unequal, suddenly de- 
creasing to 4 or 4| in *01 mm. , again increas- 
ing to about semiradius, thence decreasing to 
border. Border distinct, smooth, . 
bisinuatus. 
54. 
biangulatus. 
55. 
bulliens. 
56. 
compositus. 
groveanus. 
secernendus. 
debilis. ■ 
traducens. 
megaporus. 
profundus. 
pacificus. 
radiosus. 
fimbriatus. 
obversus. 
radiatus. 
marginatus. 
robustus. 
oculus-iridis. 
antarcticus. 
biharensis. 
