114 BIOLOGY OF THE RICHMOND RIVER, 



Lismore(l, 6, 11). Kyogle(41). 



The central nodule in all these forms is quadrate, diam. 2 or 

 4/x. 



The longitudinal furrow, 2-4 /x broad, seems (from broken speci- 

 mens) to be a lacuna in the membrane. 



Genus Vanheukckia Breb. 



VaNHEURCKIA RHOMBOIDES var. NEGLECTA(Thw.) f. MINOR, n.f. 



Forma dimidio brevior ; valvae lineares-ellipticae, apicibus rotun- 

 datis; area centrali indivisa. 



Long. 27-40; lat. valv. 7-8 }x. 



Lismore (2, 3, 6, 20). Kyogle (45). 



The larger form [Schizonema neglecta Thwaites; Nav. gracilis 

 var. neglecta (Thw.), W. & G. S. West; Nav. gracilis var. schizo- 

 nemoides V.H.) measures 50-90 x 8 /x. 



Vanheurckia cuspidata var. danaica (Grun.). 



Long. 73-80; lat. valv. 18/x. Columella broad, undivided. 



Lismore (3). 



Navicula cuspidata and its forms should be arranged under 

 Vanheurckia', there is no real difference between forms with 

 divided and those with undivided central area. 



Var. ambigua (Ehr.). 



Long. 70-75; lat. valv. 22, ap. 6/x. Apicibus ssepe levissime 

 capitatis. 



Lismore(5). Casino(14). Kyogle(41). 



Syn. Nav. ambigua Ehr. in Donkin, Br. Diat., P1.6, f.5. A'av. 

 cuspidata var. ambigua (Ehr.) Cleve. Specimens were noted with 

 a single broad columella (with incipient median line, however, 

 above and below the central nodule) and also with a double one. 

 The median line (1 true raphe or merely a furrow) in these 

 Vanheurckia forms develops generally from the centre outwards. 

 Beginning as a minute foramen on either side of the central 

 nodule (and defining it), it gradually extends outwards to the 

 terminal nodules, thus forming a double columella. Cf. Vanh. 

 (Frustulia) leptocephala Oestrup, Oest-Gronland, T. i., f.l. 



