120 BIOLOGY OF THE RICHMOND RIVER, 



Var. ALGENSis, n.var. (PL v., f.2, 3). 



Valvse breviores, prse longitudine latiores, ellipticse plus minus 

 ovatse; costis 10-12, terminalibus 3 vulgo (interdum omnibus) 

 simplicibus. Latere cingulato valde cuneato, apicibus latissimis 

 ad basin rapide attenuatis; marginibus alarum medio retusis. 



Long. 56-106; lat. valv. 34-56; lat. frust. ap. 36, bas. 20 /x. 



Lismore (5, 7, 8). Cum priori. 



Cf. G. S. West, Third Tanganyika Exp., p. 165, PI. 8, f.5; also 

 Suri. margavitacea O. Miiller, Bac. a.d. Nyassaland, p. 37, PI. 2, 

 f.l2, the latter probably a smaller size of var. algensis with the 

 costje broken up into rows of minute granules. I consider Suri. 

 plana a variation of Suri. robusta, with one end (or both) very 

 broadly rounded and a tendency to be ovate; in girdle-view they 

 are identical. The girdle-view in var. algensis is characteristic, 

 being strongly cuneate. The costpe are distinct to the centre, or 

 merely marginal according, of course, to the silicification of the 

 membrane. Some forms were noted with simple costae only, pro- 

 ceeding from marginal denticulations as in Sui'i. elegans and S. 

 ovalis. These costse do not remain simple, however, but become 

 double with growth of the frustule. S. robusta var. splendida in 

 the same water (long. 136-140, lat. 48-50 /x); Lismore (6, 7, 8, 18), 

 and Casino (14). 



Genus Nitzschia Hassal. 

 NiTZSCHiA PARADOXA (Gmel.) Grun. 

 Long. 80-100; lat. valv. 6, ap. 2 /x. (Bacillaria paradoxa 

 Gmelin). 



Var. MAJOR Van Heurck. (PI. v., fig. 4). 

 Long. 100-120; lat. valv. 8; lat. frust. 8, ap. 6 /x. Puticta 5 in 

 10 /i. 



Var. PERPUSILLA, n.var. (PI. v., f.5). 



Forma minima; valvae lineari-ellipticse, apicibus acute-rotun- 

 datis nee rostratis. 



Long. 22-40; lat. valv. 5; lat. frust. 6 /x. 



Lismore (1, 2, 6, 8, 15, 17, 20, 21), type and var. perpusilla; var 

 major (7, 8). 



