42 
Greville, on Asterolamprce. 
base of a marginal segment of an orbicular valve; while 
alternating with them were rays passing between the seg- 
ments to the margin. Perceivings thereforCj that these 
discs must either be included in the genus Asterolampra 
itself, or constitute one or more very nearly akin to it, I 
commenced a patient and prolonged examination of the 
^' Barbadoes earth/^ which extended over many months ; and 
the notes and drawings made during that period form the 
basis of the paper which I have now the honour of laying 
before the Society. 
In my former monograph I endeavoured to show that 
there was not sufficient ground for keeping up the three 
genera_, Asterolampra, Asteromphalus , and Spatangidium, and 
suggested that they should be regarded as sections of one 
genus, for which I proposed to retain the oldest name of 
Asterolampra. The first section of the genus so constituted, 
and which I considered as typical of the whole group, is 
composed of discs in which the rays are all equal and equi- 
distant, as well illustrated in the first described species, 
A. Marylandica. After carefully studying the whole series 
of the Barbadoes frustules, I have arrived at the conclusion 
that in the present state of our knowledge it is more expe- 
dient to refer them to Asterolampra, than to attempt to 
arrange any of them into a separate genus. It is remarkable 
that, with a single exception, all the species belong to the first 
section above mentioned — the exception being A. heptactis 
{Spatangidium heptactis, De Breb.), which, at the last mo- 
ment, Mr. Kitton informs me he has detected in a sample of 
the deposit obtained from Cambridge Estate.^-* 
The series of diatoms to be now described and figured is a 
peculiarly interesting one ; for, varied as is the structure in 
the twenty species formerly described, it is greatly more so 
in those under consideration. Commencing with valves 
which can scarcely be separated from A. Marylandica, we 
pass through various most remarkable modifications of the 
normal structure, until we come to individuals whose generic 
position may be almost regarded as doubtful. With the 
exception of the species just mentioned ; of a second, which 
I call A. affinis, and which comes near to A. Grevillii ; and 
of A. heptactis, the entire series is characteristic of the Bar- 
badoes deposit. They differ in many respects from the sub- 
jects of my previous paper. They are more robust, although 
generally smaller in size, highly siliceous, vitreous in appear- 
ance, with the divisional lines hard and clear. Many of them 
are very convex, especially A, Brightwelliana, which Mr. 
Rylands aptly compares to a Medusa, The segments are 
