friend Professor Allman, who omits no opportunity of adding an 
unobserved fact or a new member to biological science, noticed 
that an oyster-shell (found on a supper-table) was infested by 
some animal and vegetable parasites; among others, by some 
poor looking specimens of Chrysymenia clavellosa. On looking 
a little closer at these latter, he spied, what few but an observer 
so lynx-eyed would have discovered, some minute white dots, 
irregularly placed on the surface of the fronds. These he deemed 
worthy of examination, and laid aside the oyster-shell for that 
purpose. On submitting a fragment of the dotted Chrysymentia 
to the microscope the following day, the first trial rewarded him 
with a sight of the delicate, glassy fan which is here copied from 
his drawing. I have added a representation of the oyster-shell, as a 
memento of the discovery ; recommending to all botanical oyster- 
eaters to make a similar use of their eyes. 
The aspect of this little parasite is strikmgly similar to that of 
a Coleochete, but the calcareous nature of the cellular membrane 
seems to point to a different affinity. In the absence of infor- 
mation respecting its fructification, I can form but a guess as to 
the family im which it may most properly be arranged. In sug- 
gesting the Corallinee 1 am chiefly guided by the calcareous 
tissue: the /adit, indeed, is not unlike that of some of the 
minute Melobesia. The structure is much more simple, and, 
taking into account the stony nature of the cells, sufficiently 
peculiar to justify the formation of a new genus for the reception 
of this organism. For the genus Dr. Allman has suggested the 
appropriate name Lithocystis, and it affords me great pleasure 
to add the specific name A//manni. 
Fig. 1. An old oyster-shell, with various animal and vegetable parasites: Litho- 
cystis Allmanni, forming white specks on the frond of Chrysymenia clavellosa. 
2. Liraocystis ALLMANNI :—highly magnified. 
