NOVARA DIATOMS. 79 



be divided into two sections, the one containing forms with mar- 

 ginal loculi, the other those surrounded with marginal plates. 



Amphora kamoxthensis, f/rww.— Frustules complex, oblong, sub- 

 rectangular, or with a slight median constriction ; angles rounded ; 

 valves linear cymbiforme ; ventral margin straight; dorsal ele- 

 vated in the central part, straight, or slightly constricted ; apices 

 slightly produced; median line somewhat bi-undulate, approaching 

 the inferior margin ; central nodule transverse, dilated ; longitu- 

 dinal sulcus parallel with the dorsal portion ; stride punctate, sub- 

 radiant, 35 in. -001. PI. v. fig. 11. a. b.c. d. 



Not uncommon in shore sand from Kamortha, one of the Nicobar 

 Islands. 



I have formerly described the form as A. Grevilleana. Further 

 observations on better preparations, in which valvular veiws were 

 abundant, show that the distinct, broad, median line is constant. I 

 have occasionally observed valves greatly resembling A. Grevil- 

 leana. 



Navicula foxtis = Pinnularia fortis, Gregory. 



Var. ? opima. — Frustules broad, truncate, slightly constricted at 

 the centre ; valves broad, ovato-lanceolate, rounded at the apices ; 

 median line straight, central nodule small, oblong ; terminal nodules 

 minute, remote from the ends, striae conspicuous, non-punctate, 

 subradiant, 14 to 15 in. -001 ; a smooth space surrounds the central 

 nodule. PI. v. fig. 13. a b. 



Amongst sand from the roots of Ecklonia, from St. Paul, and 

 rare in shore sand from Auckland. 



Among all the figures known to me, the best is. one of A r . varians 

 in Alia Jour, iii, pi. 2. fig. 25. N. varians is, however, entirely 

 confined to freshwater. N. retusa, Breb., appears to be closely related 

 to this form ; but the valves are smaller, and not so broad as in 

 iV\ fortis. 



Navicula quadxisulcata, Grun. — Valves broad, ovato-lanceolate, 

 ends slightly produced, obtuse, central nodule small, oblong, striae 

 transverse, distinct, minutely punctate, radiant, 16 to 20 in. -001 ; 

 furrows longitudinal, connivent at the ends, double on each side. 

 PI. v. fig. 14 a b. 



Amongst sand, from the roots of Ecklonia buccinalis, from St. 

 Paul's, South Sea. A characteristic form that cannot be confounded 

 with any other species. It is distinguished from iV. nitescens not 

 only in form and its conspicuously punctate striae, but also in the 

 greater number of longitudinal furrows. 



Navicula suboxbiculaxis var. nankooxensis, Grun. — Costae dis- 

 tinct, 10 in. "001, alternating with a series of minute granules. 

 PI. v. fig. 16. 



In Polycystin stone, from Nankoori. 



The form, median line, and longitudinal furrow same as in the 

 type species ; the delicate rows of puncta stand between strong 

 costae, which in that form are delicate and scarcely visible. In 



