106 
GrevillEj on Asterolampra. 
cording to Ehrenberg himself) from Asterolampra in two of 
the umbilical lines common to both genera becoming approxi- 
mate and " parallel/^ and in one of the rays common to both 
genera becoming narrower than the rest. But even this dif- 
ference is not strictly maintained in all Ehrenberg^s own 
species ; for in A. Darwinii and A. Rossii the median lines 
are not "parallel/^ but cuneate. This deviation from the 
generic character is still more prominent in recently disco- 
vered species^ which^ notwithstanding^ cannot be excluded 
from this place. In my Asterolampra Dallasiana, for ex- 
ample (PI. IV, fig. 10), the median lines are campanulate ; 
and in my Asterolampra Wallichiana (fig. 11), they are 
so widely cuneate as to show a decided approach to Aste- 
rolampra as restricted by Ehrenberg. It is evident, therefore, 
that were the genus to be sustained, the character derived 
from the parallelism of these lines would have to be aban- 
doned. With regard to the form of the segments, they are 
represented as concave at the base in all Ehrenberg^s species. 
In Asterolampra Dallasiana and A. Wallichiana, however, 
they are square at the base. The angular bend in the umbi- 
lical lines which marks some species of Asterolampra and 
Spatangidium is found also in Asteromphalus in one or two 
instances. 
I have remarked elsewhere — and am glad to see that my 
view is supported by Dr. Wallich — that the character on 
which De Brebisson founded his genus Spatangidium, viz., 
the eccentrical position of the hyaline area, is far too uncer- 
tain to be relied on ; for valves are continually occurring in 
which this feature is scarcely, if at all, perceptible. And 
when this character disappears, so also does the " sub- orbicu- 
lar form of the valve. How little dependence can be placed 
upon it is well shown in S. heptactis of De Brebisson {S. 
Ralfsianum of Norman, in my former paper) . De Brebisson 
does not state the form in his description, but his figure 
represents it as broadly ovate, whereas in mine it is the very 
reverse.^ An exception, however, appears to exist in Spa- 
tangidium Arachne, which, as far as 1 have observed, retains 
constantly its round-ovate outline, as well as its highly eccen- 
trical arrangement. A better generic character than the 
latter might have been found for Bpatangidium, as Professor 
W alker-Arnott has suggested, in the median lines (Dr. Wal- 
lich^s basal ray) passing over and beyond the central point, 
so as to cause the umbilical lines to radiate from the top and 
sides of the median lines, and not from the central point 
* 'Mic. Journ./ vol. vii, PI. 7, fig. 8. 
