43 



PYXILLA. 



GENUS 96. PYXILLA (GREV, 1864), H.V.H. Emend. 



*Oa a O O O o 3 flB 

 6 o * 



^---3 



Fig. 149, 



Pyxilla Barbadensis. 



Fig. 150. 

 Kentrodis'cus Huti^aricus . 



Fig- 151- 

 Pterotkeca aculeifera. 



Frustules simple, cylindrical, pyxidiform ; valves often of unequal 

 length, showing in the centre a simple or alate apiculus. 



As we understand this genus, it includes three genera of other authors, 

 which we consider as subgenera only, differing from one another as follows : 



' Apiculus simple . 



Apiculus covered with small scattered spines 

 _ Apiculus laterally alate and branched 



. Pyxilla Grev. 



. Kentrodiscus Pant. 



. Pterotheca Grun. 



I figure here Pyxilla Barbadtnsis Grev. (fig. 149), Krtrodiscus Hungaricus, 

 Pant., (fig. 150), and Pterotkeca aculcijera, Grun, (fig. 151). All these forms 

 are fossil. 



GENUS 97. KTENODISCUS PANT., 1891. 



Valves rounded, convex, divided 

 into compartments dichotomously, 

 with margins surrounded by ellip- 

 tic hyaline spaces. Frustules 

 showing in girdle view the valves 

 very inflated, crowned with a comb 

 of alate spines fastened at the base. 



Fig. 152. Ktenodiscus Hungaricus. 



I reproduce (fig. 152) after Dr. Pantocsek Ktenodiscus Hungaricus 

 Pant., a curious fossil form from Hungary, which resembles a Prussian 

 helmet. 



