Greville_, on New Diatoms. 
67 
■unite in its composition. The central and larger space has 
round cellules^ so remotely and irregularly disposed as to 
render it unlike a diatomic structure. Then comes the cha- 
racteristic circle of large^ equal, hexagonal cellules^ which 
exhibit the singular peculiarity that the marginal angles of 
the hexagons are not quite completed. Lastly, between the 
large cellular circle and the margin the space (equal in 
breadth to the diameter of the large cellules) is filled up with 
radiating, robust, moniliform striae, which take the place of 
the narrow marginal band of puncta seen in the preceding 
species. It must be confessed that in general appearance the 
two species differ exceedingly, and it is by no means im- 
probable that the present one may be ultimately separated. 
Fenestrellaj nov. gen., Grev. 
Frustules free, disciform ; disc with a minute, radiant 
cellulation, interrupted in the middle by linear bands, com- 
posed of parallel lines of cellules, each band terminating in 
a flat ocellus. 
This genus is composed for the reception of a solitary but 
most curious diatom, the relations of which it is not easy to 
define. The groundwork of the disc is very much that of 
Coscinodiscus, being composed of radiating lines of cellules, 
with a marginal row of puncta. But a couple of circular 
ocelli, at little more than half the radius from the centre, 
although not conspicuous, are sufficiently evident, and show 
that we must look for affinities elsewhere. These ocelli are 
not processes, but definite blank spaces in the cellulation, and 
have therefore no connection with Eupodiscus or Aulacodiscus. 
Another peculiarity is a broad, linear-oblong band passing 
across the middle of the disc, and composed of about eight 
rows of cellules ; or perhaps it would be more correct to say 
that two opposite sets of rows of cellules meet at their bases 
in the centre, and at the other extremity converge as thev 
terminate in the occelli, with which they are evidently con- 
nected. There is no umbilicus, the band of cellules intercept- 
ing, as it were, the meeting of the radiating lines, the only 
indication of the central point being a slight interruption in 
the continuity of the cellules, not sufficiently definite to con- 
stitute a character. The convergence of these lines of cellules 
towards the ocelli seems to point to some alliance with Au- 
liscus, but, on the other hand, there is none between the 
mastoid processes of that genus and the ocelli of the present 
one. 
