522 



ACTINOCYCLUS. 



GENUS 186. ACTINOCYCLUS EHR, 1840. 



V^T^-^-v,, 



Fig. 276. Actinocyclus Ralfsii. 



Valve orbicular, elliptic or rhomboidal- oblong, convex, having a 

 marginal or submarginal pseudo-nodule, frequently furnished with 

 small marginal or submarginal spines ; puncta in radiating rows of 

 unequal length, usually leaving subulate hyaline spaces. Frustule 

 disciform. 



ANALYSIS OF SPECIES. 



Valves 

 circular. 



Valve 



usually 



iridescent at 



a low 

 magnifica- 

 tion, 

 puncta very 

 visible. 



Hyaline f Subulate spaces very broad, pro- 

 spaces of ducing the appearance of well- 

 the marked concentric zones ; 



valve \ puncta very vigorous . A. Ralfsii. 



clearly 

 subulate- Subulate spaces very narrow ; 



acute. i puncta more delicate . A. Ehrenbergii. 



Hyaline spaces not subulate ; puncta strong, 



forming undulated concentric lines . A. crassus. 



Valve not iridescent ; puncta very delicate ; subulate spaces 



very feeble or absent . . -A. subtilis. 



Valves elliptic 



. A. Roperii. 



The genus Actinocyclus includes about 60 species, found mostly in a living 

 state, and inhabiting all parts of the world. 



