126 BIOLOGY OF THE RICHMOND RIVER, 



triangular marginal interspaces, or in arcs (decussating) from 

 point to point of the circumference. In some specimens, they 

 appear as arcs or in irregular radiating lines according to the 

 focus. Sometimes, the puncta are very distinct and separate, at 

 others, obscure or inclined to be confluent, at others, again, very 

 delicate and hardly visible, sometimes, apparently absent. 



There is a great general likeness between Coscinodiscus lacus- 

 tris and Cyclotella Meneghiniana var. convexa, and I am not at 

 all convinced that they are not stages of the same plant, and 

 that this, the only freshwater Coscinodiscus, is not, as W. Smith 

 considered it, a Cyclotella. 



Yar. PKLLUCIDUS, n.var. 

 Valvse membrand glabnl, striis punctisque nullis. 

 Diam. observ. 52-61 /x. 



Yar. STELLATUS, n.var. (PI. v., f.27). 



Yalvae membrana glabnl , area centrali nuda, granulis margin- 

 alibus distinctis, striis spatio distantibus. Unicum frustulum 

 tantum vidi. 



Diam. observ. 50 /x, striae long. 1 5 /x. 



'?Syn. Cyclotella Kiitzingiana Kirchner, in Forbes and Richard- 

 son, Biology of the Upper Illinois River, PI. 85, f.l. Each of 

 the striae proceeds from a marginal granule, probably intermediate 

 striae form between the others. No doubt an abnormal out- 

 growth of the foregoing. 



Yar. DENTicuLATUS, n var. (Pl.v , f.28). 



Yalvae granulis marginalibus in denticulos productis, inter se 

 paullo magis distantibus. 



Diam. 44-55 /x. 



The marginal denticulations are 3/x apart from centre to 

 centre, in the type 2 /x. Is this identical with Stephanodiscus 

 Hantzschianus Grun., in Yan Heurck, Diat., p.520, P1.23, f.662?. 



Yar. PAPILLATUS, n.var. (PL v., f.29). 

 Yalvae intra margines papillis humillimis 8, pari intervallo 

 inter se distantibus instructae. Unicum frustulum tantum vidi. 

 Diam. observ. 50; crass. 20 /x. 



