ill!Ill

Fig. 236.
A. (Polymyxus) fulchellus.
ACTINOPTYCHUS. 495
Fig. 237. A. (Schuettia) annulatus.
Valves circular, rarely triangular, with triangular compartments
alternately smooth, elevated or depressed, structure usually alveolar
and with a central polygonal umbilicus. Alveoli placed on a punctate
lamina (which is sometimes the only one present), with or without
hyaline spaces and small submarginal spines
at the circumference of
the valve. Frustule disciform, undulated, divided into compartments,
with girdle face narrow.
The genus Aciinoptychus is widely extended, embracing more than 100
species, the greater number of which are fossil, and remarkable for their
beauty or elegance. A typical valve of A. undulatus Ralfs. is represented in
figure 232.
Several genera have been created at the expense of the genus Actinopty-
chus, amongst which we may mention :
Debya Pant., 1886 (non Rattray) (fig. 233), drawn from one of my
photographs, which is founded on the interior valves of A. undulatus Ralfs.
I have frequently found these valves in the mud of the Scheldt and the
sediment of the North Sea, and I have in my possession specimens where
this internal valve can be clearly seen through the normal valve.
Gyroptychus contabulatus. Ad. Schm., described hereafter among
the Asterola/nprea-, is probably only the interior lamina of an Aciinoptychus.
Omphalopelta Ehr., 1844, comprehends the Aciinoptychus with a
spine or process in alternate compartments. A. undulatus is very often found
in this state.