12 
Greville_, on New Diatoms, 
the marks in tlie following species seems to contradict sucli 
a supposition. In tlie one under consideration they are 
more uniform^ constituting, in fact_, a band of short, thick, 
radiating, dark lines. Between this band and the margin the 
puncta are much more minute, and might almost be called 
moniliform striae. 
Aulacodiscus pellucidus, n. sp., Grev. — Disc pale, with 
minute, not very close, radiating puncta; furrows incon- 
spicuous j processes numerous (8) , at some distance from the 
margin, within a narrow, oblong, blank area ; margin with 
moniliform strise, and a very slight inflation beneath the 
processes. Diameter. 0045'' (fig. 5). 
Hab, Barbadoes deposit, Cambridge estate ; C.Johnson, 
Esq. 
In this species the structure is not so minute as in the pre- 
ceding, and the furrows can be more easily traced. The pro- 
cesses are more numerous, and the vacant spaces in which 
they are situated are of a quite different shape ; and, what- 
ever may be the cause of the little dark markings, there can 
be no doubt that their different shape and arrangement 
indicate a specific difference in the two objects. A convex, 
shaded line, opposite to and beneath the processes, seems to 
show a slight inflation ; and this line, continued in a fainter 
degree and straight direction from one process to another, 
gives a somewhat angular character to the ridge. 
Aulacodiscus orientalis, n. sp., Grev. — Disc coloured, very 
convex; processes numerous (7 to 15, or more), cylindrical, 
submarginal ; umbilicus circular ; structure minutely and 
distinctly cellulate, the cellules arranged in both radiating 
and concentric lines, which suddenly pass into moniliform 
strige at the margin. Diameter -0045" to '0060'^ (PI. II, fig. 6.) 
Hab. Ceylon ; Dr. Macrae. 
A most charming diatom, delighting the eye with its 
exquisite symmetry. At first sight it is so like A. Oregayius, 
that one is apt to reject at once its claim to novelty. At the 
same time, a single really searching glance is sufficient to 
decide the question. Of A. Oregaims, Mr. Balfs remarks. 
Under a low power its minute granules appear arranged in 
waved or oblique lines, but imperfectly radiant under higher 
powers.-*^ In the present species, on the contrary, the 
structure is essentially and exquisitely radiant, whatever 
power may be used. In the description of A. Oreganus the 
term granules is appropriately used, as the structure is 
apparently composed of granules; in A. orientalis it is 
impossible to use such a term, as there is not the very 
slightest appearance of granules, but simply a sort of 
