112 
Greville^ on Asterolaynpra. 
divided. In the series already referred to_, as communicated 
by Professor Walker- Arnott, the following arrangements of 
these lines occur. (1.) In a valve with seven rays_, one 
line is simple,, six united in triplets ; so that only three 
lines actually radiate from the central point. (2.) A valve of 
eight rays (fig. 6) : two simple lines and two triplets ; four 
lines therefore radiate from the central point. (3.) Another 
valve with eight rays : one simple line^ two forked and one 
triplet; four lines^ as before^ radiating from the centre, but 
by a different combination. (4.) A valve with nine rays 
(fig. 7) : two simple lines, two forked and one triplet ; in 
this case the divisions occur at a considerable distance 
from the umbilicus, and five lines emanate from the central 
point. (5.) A valve with ten rays : no simple line at all, but 
two forked and two triplets; only four actually radiating 
from the centre. (6.) A valve with eleven rays (fig. 8) : 
one simple line, two triplets, and one quadruplet ; still only 
four proceeding directly from the umbilical point. It will be 
obvious from the above statement, that there is a decided 
tendency in the umbilical lines of this species to arrange 
themselves in triplets. I regret that I have not space to 
admit of the entire series being engraved, but the examples 
I have selected will afford a good idea of the whole. It is 
worthy of observation that the valve I have represented at 
figure 6 seems, on a momentary glance, to possess what I 
have called median lines, which enclose Dr. Wallich^s " basal 
ray" (" from the true rays being always arranged around or 
upon it") ; but this is a deception. Median lines, according 
to my view, cannot exist apart from a median ray, and con- 
sequently are not to be found in this section of the genus. 
In the present instance it will be perceived, by a comparison 
with figures 7 and 8, that the appearance is caused by two 
triplets of umbilical lines happening to adjoin each other. 
The same effect is twice repeated in figure 8, only not quite 
so conspicuously. Dr. Wallich proposes to substitute the 
term " basal" ray for median or " obsolete" ray ;^ but as 
there is no instance on record of more than one median ray 
occurring in the same valve, he must use the term in a more 
enlarged sense in his highly interesting paper, when he 
ascribes three basal rays to the species he has done me the 
honour to associate with my name. In one of Professor 
Walker- Arnott^s slides is an abnormal valve of A, variabilis 
with the hyaline area very eccentrical, and the whole having 
exactly the appearance as if it had been intended for a 
* 'Trans. Mic. Soc.,' vol. viii, p. 45. 
