GENUS 165. 



GYRODISCUS. 503 



GYRODISCUS WITT, 1885. 



Valve discoid, some- 

 what cap shaped ; 

 margins very slightly 

 elevated, centre much 

 raised into a conical 

 apiculus, with trun- 

 cate apex. Arising 

 from the apiculus 

 are rays bent in op- 

 posite directions near 

 the two apices of the 



Fis:. 248. Gyrodiscus Vortex, j. 



& 4 J same diameter. Sur- 



face of valves very delicately granular, apparently hyaline. 



This genus includes only two species, G. Vortex Witt. (fig. 248) found 

 by Dr. Witt, at Simbirsk, and by Dr. Pantocsek, at Kusnetzk, and G. 

 Hungaricus Pant., found in Hungary by Dr. Pantocsek. 



Group Asterolampra (Ehr., 1844), Ch. em. Valve with 



hyaline area, divided by straight rays, arising either from the 



centre, or Irom a central rosette, and terminating at the base 



in areolate marginal segments ; such segments being formed 



by the sub-division of the margins by means of a continuation 



of the hyaline area. 



The Group Asterolampra comprehends the genera Asterolampra 

 Asterotnplialus, as well as the doubtful genus Asterodiscus and the pseudo- 

 genera Actinogonium and Liostephania. 



The genus Actinogonium consists of the 



internal valves ot Asterolampra, and by 



examining carefully several valves of 



Asterolampra these internal valves can be 



seen. They can also be recognised by the 



figure given by Greville of his A. punctata 



(T.M.S., 1862, pi. 8, fig. 32). The figure in 



the text (fig. 249) represents a similar 



internal valve, which Ehrenberg has named 



Actinogonium Seplenarium. 

 Fig. 249. Actinogonium Septetiarium. 



