Shadbolt on New Forms of DiatomacecB. 
J7 
American Journal of Science and Art,' vol. xlviii. ; a copy of 
the paper is in the library of this Society, it having been pre- 
sented by the late Mr. Edwin Quekett. The Port Natal 
species differs in many respects from A. marilandica, as the 
following description will show : — 
Frustules disciform, slightly convex, cellular (?), elegantly 
marked around the margin with 7 or 11 segments of an 
elliptical or parabolic outline, radii proceeding from the 
centre to the apex of each segmental curve, and strength- 
ened with bracket-like projections. The aspect is not unlike 
an ornamental wheel, the radii forming the spokes. The seg- 
ments are regularly and minutely divided into dots or cells (?), 
but it is necessary to use a high power and careful manipula- 
tion to display them ; when properly shown, however, nothing 
can well be more exquisitely beautiful. There is a very no- 
ticeable peculiarity in the number of the segments ; in every 
specimen I have seen, being either 7 or 11 (a few only of the 
latter number), and in the normal state the two valves, as far 
as my observation extends, are, without exception, disposed 
alternately, that is, that a segment of the superior valve always 
corresponds to an interspace of the inferior one, and vice versa. 
I have named this species A. impar, from the odd number of 
segments. Fig. 14 is a representation of this beautiful frustule. 
A species of another genus, established by Professor 
Baily, Climacosphcenia, is shown at figs. 15 a and 15 5, b 
being the lateral view, and a the front view, in which the 
ladder-like divisions more resemble the links of a chain than 
in the only other species I have seen : I have consequently 
called it Cl. catena. 
Two very interesting forms, by no means rare in this very 
rich gathering, belong to a genus that has been described, 
under the names of Zygoceros and Denticella^ the latter by 
Professor Baily, and as they clearly differ from the former, as 
may be seen by the most casual observer on inspecting fig. 
16, which is a single frustule of a true Zygoceros, moderately 
common in this collection, I shall adopt the latter designation. 
I have only seen them either single or in pairs, having just 
completed the process of self-division, having a somewhat 
persistent connecting membrane. Front views are shown of 
the two new species in figs. 16 and 17. The side view is more 
or less elliptical in outline at the junction of the two valves, 
but sections in almost every other plane parallel to this would 
present a different figure, owing to the protuberances shown 
in the front view. In both species there arise from the cen- 
tral inflations two slightly curved spines from each valve, 
which, as in Triceratium, &c., in the process of self-division, 
VOL. II. e 
