Greville^ on Asterolampra. 
iia 
Spatangidum. It lias six rays^ the lower one much the 
longest; the upper one shorty and the lateral ones slightly 
curved downwards. This accidental deviation from the 
ordinary arrangement of the valve in this species is imma- 
terial^ except as an additional illustration of the tendency 
in individuals belonging to the different sections of the 
group to partially assume the general appearance of each 
other. 
4. Asterolampra GrevilUi. — Areolated segments square at 
the base ; rays numerous ; umbilical lines divided and ar- 
ranged in parcels or groups of from two to five lines each. 
Diameter about -0034". (PL IV, fig. 21, an abnormal 
valve.) 
Asteromplialus Grevillii, Wall. Trans. Mic. Soc, vol. viii, p. 47, Pi. 2, 
fig. 15. 
ffab. — Rappahannock Deposit, United States, Mr. E. W. 
Dallas. Indian Ocean, Dr. Wallich. Monterey stone, 
Professor Walker- Arnott. 
The uniform character of the rays brings this species into 
the present section. The examples originally discovered by 
Mr. Dallas, and which I had described in MS. as unques- 
tionably distinct, I have little or no hesitation in now referring 
to this place. Although no character can be strictly drawn 
from the number of rays, yet it would seem that in this 
diatom they are so numerous as to give it a peculiar appearance. 
The umbilical lines, as they radiate from the central point, 
are very few ; bat they almost immediately divide in such a 
way, that a group of lines seems to be supported, as it were, 
by a single short stalk. The frustule figured by Dr. Wallich 
has thirteen rays ; the umbilical lines are combined into 
three groups ; the three little stalks which support them alone 
radiating Irom the central point. One of the American 
specimens, of which I had prepared a drawing, contains 
fifteen rays ; and the umbilical lines are combined into four 
groups, supported by as many little stalks. Another of the 
American specimens contains seventeen rays. The one with 
fifteen rays has four, which Dr. Wallich would call " basal 
that is, they unite at the umbilicus exactly in the same 
manner as do his three " basal rays in his figure of the 
present species. Consequently, if I am right in considering 
the American and Indian individuals as identical, the species 
might be said to possess an indefinite number of such rays. 
But, as I have already remarked, this arrangement of the rays 
admits of a difi'erent and more satisfactory explanation. At 
figure 21 (PI. IV), I have introduced a valve, from the 
