O’MEara—Report on the Irish Diatomacee. 271 
Systephania anglica, Donkin, Q.J.M.S., 1861, p. 12, Pl. i., 
fig. 14. 
Stomachs of Ascidians, Roundstone Bay, Co. Galway. 
Odontodiscus hibernicus. N.S. Marine. 
Disk about ‘0018 in diameter; areolate ; areoles round, decussately 
arranged, reaching the circumference ; teeth more numerous than in 
former species, and shorter. (Pl. 27, fig. 7.) 
~ Stomachs of Ascidians, Roundstone Bay, Co. Galway. 
A. Frustules symmetrical. Valves not circular. 
Famity II. BIDDULPHIEA, Kiitz. 
Valves lanceolate, in some cases nearly orbicular, furnished with 
distinct processes and spines; connecting zone largely developed in 
full-grown specimens. In such species as have been seen in a living 
state the frustules are united in filaments. 
This group, established by Kiitzing without any very distinct defini- 
tion, embraced the following genera, Isthmia, Odontella, Biddulphia, and 
Zygoceros. Ralfs, in Pritchard, adopts the same system of grouping, 
adding to those above named two other genera, Hemiaulus, and Hy- 
drosera, but gives more distinct characteristics than the former author. 
His diagnosis rests mainly on the convexity of the frustules, in con- 
sequence of which the lateral valves ‘‘enter largely into the front 
view,’ and onthe development of processes on the valves. Grunow 
adopts the group with no more distinct definition than the following. 
‘Side view longish, or having three, four, or more angles,” and in- 
cludes in it four genera, namely, Isthmia, Biddulphia, Amphitetras,and 
Triceratium. Heiberg marks the group by the fact of the processes 
springing from the valve obliquely outwards, and places under it the 
genera Cerataulus, Biddulphia, Triceratium, Amphitetras; and in a 
sub-group named Biddulphiee cuneate, the genus Eucampia also. 
Immediately connected with the Biddulphiee, this Danish author 
places another group, the Hemiaulide, mainly distinguished from the 
former by this one feature, that the processes, instead of springing 
from the valve obliquely, are placed at right angles with the plane of 
the base. 
The genus Isthmia which Kiitzing, Ralfs, and Grunow include in 
the Biddulphiez, differs considerably in these respects, that the frus- 
tules on the front view are not symmetrical, and the valves are not 
furnished with processes, the structure which Ralfs regarded as such 
