1888-89.] Mr John Rattray on the Genus Coscinodiscus. 609 
The clear radial areas in this species recall those of Aulacodiscus 
acutus, Rattray {Jour. Roy. Micr. Soc ., 1888, p. 368; Jour. QueJc. 
Micr. Cl . , vol. iv. ser. 2. (1889), p. 38, pi. iii. fig. 4). 
Artificial. Key . 
( Surface with 8 submarginal bullations and a large 
-j central rosette of 3 areolae, .... 
Weissfiogii. 
(No such bullations, 
2. 
{ Irregular radial distinct bent costae passing from 
-! centre to border, sometimes branching, . 
theskelos. 
[No such costate lines, 
3. 
f Markings crowded on one half of valve, on other 
J half in distant curved rows, converging to a 
J small excentric area, ..... 
sphoeroidalis. 
[Markings otherwise, 
4. 
f Surface with 2 lateral obtusely conical plications 
4 meeting at centre, ...... 
polurrhaptos. 
( No such folds, ....... 
5. 
f A narrow hyaline band, sometimes tapering out- 
j wards, running from centre towards border, 
j Markings towards ends of bands in curves, 
j convex towards centre, and symmetrical with 
j respect to the band, ..... 
cocconeiformis. 
INo such cocconeoid structure, .... 
6. 
/ Surface without low undulations, 
7. 
\ Surface with low undulations, .... 
8. 
/ Central space absent or minute, 
9. 
\ Central space present and more evident, . 
10. 
f Markings non-fasciculate, 
11. 
-J Markings obviously fasciculate, .... 
12. 
( Markings obscurely fasciculate, .... 
13. 
' Markings areolate, round, granular on a distinct 
unilateral lunate depression. A rosette usually 
present, 
lunatus. 
Markings angular, at centre 3J, at border 4, in 
*01 mm. ; rows oblique, decussating, forming 
many distinct areas on surface. Border broad, 
distinct, 
implicatus. 
Markings of 2 kinds, the larger areolate unequal, 
2 to 2^ in ’01 mm., prominent, within these 
the smaller more faint, ..... 
bisculptus. 
INo such areas or markings, .... 
14. 
' Valves reniform, 
reniformis. 
Valves diamond-shaped, ..... 
15. 
Valves elliptical, 
16. 
Valves circular, ...... 
17. 
Valves obtusely angular. Markings towards 
centre 3, at border 4 to 4|, in - 01 mm. . 
Valves subcircular. Markings angular, towards 
centre 8, gradually increasing outwards for f 
radius to 6, on a distinct band adjacent to 
border punctiform 10 to 12, in - 01 mm. ; sub- 
l ulate spaces evident near marginal band, 
subangulatus. 
moronensis. 
vol. xvi. 29/10/89 2 Q 
