5*4 



15RIGHTWELUA. 



Sect. II. Brightwellie.e. Valves cellular, with one or 

 more rows of marginal or sub-marginal cells, differing 

 (generally much larger) from the other cells of the valve ; or 

 with the sculpture of the median portion different from that of 

 the margins. 



GENUS 177. BRIGHTWELLIA RALFS., 1861. 



Valves circular, with cellular structure ; 

 cells unequal, those of the margin smaller 

 than those of the centre, and separated 

 from one another by a ring of much 



Fig. 266, Brighhvellia hyperbvrea. 



larger cells. 



This beautiful genus possesses seven 

 species, which are all fossil, two of them 

 (including B. hyperborea Gritn.), (fig. 266), 

 have also been found in marine dredgings or 

 soundings. 



GENUS 178. HETERODICTYON GREV., 1863. 



Valves circular, finely punctate, 

 with a central rosette of medium 

 sized cells, and a ring, quite margi- 

 nal, of large elongated cells. 



This genus consists of a single 

 species, H. Rylandsianum Grev., 

 figured in the text, found in the Cam- 

 bridge Estate Deposit, Barbadoes, by 

 C. Johnson. 



Fig. 267. Ilcterodictyon Rylandsianum. 



