388 
PROCEEDINGS OF THE SOCIETY. 
bringing so large a number of Microscopes to the meeting and placing 
them at his disposal. 
The following is compiled from the descriptions referred to. 
1. Actinoptychus cinnulatus. — From Whampoa, Canton River. On 
account of its triangular form this diatom was at first classed amongst 
the Triceratia, but closer examination has caused its removal to the 
genus Actinoptychus , one striking peculiarity of which is the division 
of the valve into compartments or segments, by the alternate elevation 
and depression of the valve round a central “ umbilicus.” As a rule 
the Actinoptychi are circular, but there are several exceptions to this 
rule, the present form being a good example. The centre diatom is a 
frustule placed on edge. 
2. Arachnoidiscus Ehrenbergi.— Halved valve. This is mounted 
on edge, and shows the form of the ribs on the inner side of the valve 
supporting the outer casing, thus economising to a certain extent the 
amount of silex required. 
3. Arachnoidiscus ornatus. — In situ on coralline,' the latter having 
been decalcified. This slide shows the pill-box form of the diatoms in 
every conceivable position, some of them being doubled ready for sub- 
division, as can be seen by viewing them edgewise. Mounted in soft 
balsam. 
4. Aulacodiscus margaritoceus. — Believed to be from Pisagua, West 
Coast of South America. The specimen shown is an abnormal one in 
regard to its markings. Usually the cells are so crowded together that 
they become polygonal from mutual pressure, but where they are dis- 
tinct and isolated they retain their rounded form. Many of “the cells 
are comparatively large, and by a little careful focusing the “ eye-spot ” 
to each can be distinctly seen on the under side of the valve. 
5. Aulacodiscus Petersi. — From shell refuse, Panama. This is 
shown as a representative of a large and beautiful genus, a monograph 
of which by Mr. John Rattray was published in the Journal of this 
Society in June 1888. The diatoms on this slide are very perfect, not 
one of the processes being broken off. 
6. Aulacodiscus Sturti. — From the stomachs of tinned oysters sent 
from Japan to the Fisheries Exhibition. This form can be used as a 
test object, but is not now shown as such ; the finer markings are be- 
tween the “ dots,” particularly towards the centre. A portion of a valve 
highly magnified is illustrated in the last edition of 4 Carpenter ’ by Dr. 
Dallinger. This diatom is to be found with 3, 4, or 5 processes, 4 being 
the most common, and 5 rather rare. I here show one with 6 processes, 
the only one I have ever found, but they are arranged irregularly, and 
undoubtedly this valve is an abnormal form. 
7. Aidiscus oamaruensis. — From deposit at Oamaru, New Zealand. 
This is a very fine form of Auliscus. The centre frustule shows that 
the processes of the valve on one side of the frustule alternate with those 
of the valve on the other side. I find this to be a general rule with all 
valves having processes. 
8. Auliscus spinosus. — From borings of an artesian well, 406 feet, 
Atlantic City, New Jersey. Five valves are arranged together, with a 
sixth a little below, placed on edge, showing the other view of the pro- 
cesses. 
