ACTINOPTYCHUS. 



495 



Fig. 236. 

 A. (Polymyxus) fulchellus. 





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. 



