122 
Greville^ on Asterolampra . 
A. heptactis, and A. Arachne, the number of rays maybe more 
constant than is generally the case in the group. The 
areolation is rather large. 
18. Asterolampra heptactis. — Segments square at the base; 
rays seven^ six of them broad_, linear^ subarcuate^ the median 
one in a broad shallow groove ; umbilical lines with a 
ramulus proceeding from each angle of the bend ; areolation 
large. Diameter -0018" to -0070". 
Spataugidium heptactis, De Bieb., Bull. Soc, Linn, de Xormand., 
vol. iii, pi. 3, fig. 2. 
Spatangidiuin Ralfsianum, Norm., Grev. Mic. Jouru., vol. vii, p. 161, 
pi. 7., figs. 7, 8. 
Hab. — Peruvian Guano^ De Brebisson. Californian Guano, 
K. G. Atlantic soundings, Mr. Roper. 
The extraordinary discrepancy between the figure, with part 
of the character in De Brebisson^s paper above quoted, and 
the numerous specimens of the diatom itself, which I had 
examined^ led me formerly to regard Mr. Norman^s Spatangi- 
dium Ralfsianum as a distinct species. The broadly ovate 
outline of the valve delineated by De Brebisson, and the state- 
ment in his specific character, that the median ray was the 
longest, were opposed to my own experience; for I had ever 
found the valve broadest in the transverse direction, and the 
two lower lateral rays the longest. I still consider that my 
figure 8, above quoted, is typical of the species, as it agrees 
with the vast majority of specimens. While, however, I was 
supported in my view by some diatomists, others were 
against me, and I am at length satisfied that we had the 
same organism in view. Among some careful drawings of 
his own making, which Mr. Boper kindly permitted me to 
consult, are two of this species, and in one of them there is a 
slight approach towards a broadly ovate outline, and the 
median ray is the longest ; but this is decidedly an exceptional 
case, unless, indeed, the Peruvian frustules differ in contour 
from those of California. There is a curious feature in this 
species which I did not formerly notice : the very slender 
ramuli which proceed from each angle of the bend in the 
umbilical lines terminate at the angles of the areolated 
segments, in a line with the margin of the broad rays ; the 
consequence of which is, the two small spaces enclosed by 
these ramuli, at the base of each of the segments although 
they form a part of the hyaline area, are excluded from the 
basal portion of the ray. It may be observed also, that as in 
this fine species, as well as in A. Roperiana, the angular bend 
is distinctly connected with a system of ramification, it may 
