Geeville, on New Diatoms. 123 
AULACODISCUS. 
Aulacodiscus sparsus, n. sp., Grev. — Small; disc with 4 
linear-oblong, submarginal processes ; granules minute, 
coloured, so remote as not to be conspicuously radiate ; 
umbilicus a subcircular blank space ; furrows becoming 
gradually wider as they approach the processes ; margin 
with a row of puncta. Diameter -0030'". (Fig. 6.) 
Hab. Barbadoes deposit, Cambridge estate j in slides com- 
municated by C. Johnson, Esq.; extremely rare. 
The only species with which the present very beautiful 
diatom can be compared is A. Kilkellyanus, which it re- 
sembles in the disc, having a general appearance of being 
sparsely filled with granules, while it is not much inferior in 
size. But in that species the lines of granules are conspicu- 
ously radiate, the sparse appearance depending upon the 
distance between the lines, the granules themselves being 
arranged in a pretty close series. The number also of pro- 
cesses in the same species is constantly three. In our new 
species the sparse character arises from the distance between 
the individual granules in the lines, which is so great that 
the radiation of the lines does not strike the eye at once, 
while the granules get disposed into half-concentric wavy 
lines, which have a beautiful effect. The number of processes 
is four. 
Cestodiscus. 
Cestodiscus pulchellus, n. sp., Grev. — Disc circular, very 
convex, with minute, remote, radiating puncta, becoming 
irregularly crowded, and slightly less in size towards the 
margin; processes numerous; margin, as well as the space 
between it and the granules, striated. Diameter '0030'^ 
(Pig. 5.) 
Hab. Nankaurie deposit, Nicobar Islands; in a slide 
kindly communicated by George Norman Esq. ; very rare. 
Distingaished by the remote punctation, which consider- 
ably neutralizes the effect of the radiating character. In the 
centre the granules are somewhat loosely disposed. Towards 
the margin the radiating granules pass abruptly into a band 
of others, crowded and irregularly arranged, from the 
outer edge of which band the processes arise, sixteen or more 
in number. Margin strongly defined and conspicuously 
striate. 
Cestodiscus Stokesianus, n. sp., Grev. — Disc circular, witli 
