Greville, on Asterolampra. 
Ill 
mentioned^ that these lines are to be considered mainly as 
ribs or bars of support. No species has so wide a range with 
regard to size as A. Marylandica. The smallest that has 
come under my notice is a specimen belonging to Mr. Roper^ 
of Shadbolt^s A. impar, which is only -0018". 
2. Asterolampra Rotula, n. sp. Grev. — Areolated segments 
nearly square at the base ; umbilical lines simple^ or forked 
close to the central point. Diameter '004^". (PI. III^ fig. 5.) 
Hab. — Monterey stone^ Professor Walker- Arnott. 
It is with considerable hesitation that I venture to oficr 
this diatom as distinct from the following^ and should not 
have done so but for the opportunity afforded me by Professor 
Walker- Arnott^ of inspecting a series of that species. I 
find, on a close examination, and after making drawings of a 
number of specimens, so uniform an adherence to the cha- 
racter furnished by the base of the segments, that I cannot 
at present bring myself to regard the present form as a 
variety. At the same time it may be held as only provision- 
ally independent. The segments are somewhat square at the 
base, and the linear portion of the rays commences abruptly 
at the margin of the hyaline area ; whereas, in the following 
species, the linear portion of the rays assumes a triangular 
figure before leaving the hyaline area, in consequence of the 
very different outline of the base of the segments. The 
umbilical lines of the two are much alike ; those of the 
species under consideration showing a disposition to divide. 
It will be perceived that one of them, immediately after 
leaving the central point, separates into three branches. 
3. Asterolampra variabilis, n. sp. Grev. — Areolated seg- 
ments, with a dipping angle at the base ; upper part of the 
basal portion of the ray triangular; umbilical lines simple, 
forked, or in triplets. Diameter '0028'' to -0048" (PI. Ill, 
figs. 6—8.) 
Hab. — Monterey stone. Professor Walker-Arnott. 
The most characteristic feature, as I conceive, of this 
diatom, arising from the form of the basal portion of the 
rays, and consequent angular base of the segments, has been 
referred to in my remarks on the preceding species. The 
result of this character is a very beautiful rosette-like contour 
of the hyaline area, and constant in all the specimens I have 
seen. The umbilical lines, also, are remarkable. In A, 
Marylandica they are, as we have seen, normally simple, 
being rarely (one or two only) forked. In the species now 
before us, the reverse is the case. In the great majority of 
instances the lines are forked or in threes ; so that in the 
same valve there will seldom be more than two of them un- 
VOL. VIII. 
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