Greville^ on Aster olamjwa. 
107 
itself^ as in Asteromphalus. A most remarkable species^ how- 
ever, belonging to the Indian Ocean sonndings — my Aster o- 
lampra Roperia7ia (PL IV, fig. 14) — seems to form a connect- 
ing link, not only between these two genera, bnt including the 
Asterolampra of Ehrenberg itself. It will be seen at a glance 
that the plan, so to speak, of the valve is far more that of 
Asteromphalus than of Spatangidium. In the circular out- 
line, in the centrical hyaline area, radiation of the umbilical 
lines, approximation of the median lines, and in the median 
ray, it is an Asteromphalus. In the single circumstance that 
the median lines pass slightly beyond the central point, form- 
ing a little imperfect circle round it, is the frustule, a Spa- 
tangidium. The median lines in this species present some 
additional curious features. But for the intervention of the 
little imperfect circle, which may be compared to the nave of 
a wheel, the umbilical lines would meet at precisely the 
central point. Immediately beneath the imperfect circle the 
median lines contract into a sort of neck, and then, instead 
of continuing to be approximate, as they ought to do for a 
Spatangidium, or parallel, as Ehrenberg would require of them 
for an Asteromphalus, they diverge, and by a curve reach the 
edge of the hyaline area at points almost equidistant between 
themselves and from the adjoining umbilical lines. In this 
last character (sub-equidistance of the termination of the 
median lines), as well as in the sub-equidistance of all the 
rays, the median one included, the frustule is very nearly an 
Asterolampra. The valve in my Asterolampra Shadboltii is 
also circular, and, but for the median lines passing slightly 
beyond the central point, would in every other respect belong 
to the Asteromphalus section. In Asteromphalus Brookei, 
likewise, of the late Professor Bailey, the valve, if not actually 
circular, appears to be so to the eye, and the median lines, 
which somewhat resemble those of Asterolampra Roperiana, 
scarcely pass beyond the central point. Enough has been 
said, perhaps, to illustrate the transition of these genera into 
each other ; and we may now proceed, in accordance with the 
views advocated, to give a systematic arrangement of the 
known species. 
Asterolampra, Ehrenb. 
AsTEUOMPHALUs, Ehr. Spatangidium, De Breb. 
Frustules simple, two-valved, disciform. Valves orbicular 
or sub-orbicular (in one case oblong) ; central area hyaline, 
and furnished with radiating lines, each of which terminates 
at the base of an areolated marginal segment ; while, alter- 
