6 P. T. CLEVE, ON SOME NEW DIATOMS. 
3. Pleurosigma (Donkinia?) longissimum Cu. N. Sp. 
Very long and narrow, linear; ends obtuse. Median line straight in the middle. 
but curved in the last third part from the central nodule. Strie in two sets crossing 
each other in right angles, transverse 18*/,, longitudinal 21 in 0,01 mm. Colcur 
pale straw. 
Length of the frustule 0,17 mm. Breadth 0,0083 mm. 
PL I, fig: 8 a. */;3 6 dtrueture *°°"/,. 
Balearic Islets rare (leg. Dr. SOpERLUND). 
Rhoicosigma Gruy. 
1. Rhoicosigma mediterraneum Ox. (in Grun. Micr. Journ. 1877, p. 182). 
Narrow lanceolate, with acute ends. .Median line strongly bent in the first third 
part from the central nodule, afterwords straight. Strie longitudinal and transverse. 
The longitudinal strie are very fine, about 27 in 0,01 mm., the transverse 18°/, in 
0,01 mm. 
Length 0,18—0,21 mm. Breadth 0,0225 mm. 
Pl. I, fig. 9, °"/,. a. and b. valves, ce. structure 7°°°/,. 
Balearic Islets rare (leg. Dr. SépERLUND). 
Navicula Bory. 
1. Navicula (Fluminensis var.?) Floridana Ou. N. Sp. 
Elongated, slightly constricted in the middle, ends rounded. Strizw not distinctly 
punctate, parallel, 15 in 0,01 mm., closer near the ends, 20 in 0,01 mm., absent from 
the middle part of the valve, not reaching the median line, which is surrounded by a 
narrow, linear area. 
Length 0,045—0,075 mm. Breadth 0,01—0,012 mm. at the constriction 0,08— 
0,009 mm. 
Fl TL ee De OP. 
Florida coast, near Pensacola Harbour (in a gathering sent by Mr. Fxsicur). 
2. Navicula cruciata Cu. N. Sp. 
Oblong, slightly contracted at the centre. Striaw 12 in 0,01 mm., parallel, costate, 
smooth or indistinctly granulate, absent from the middle part of the valve, not 
reaching the median line. 
Length 0,087 mm. Breadth 0,017 mm. at the middle 0,014 mm. 
Pi Bg ee 
I have found this species in a sample, said to be from Greenland, but as it con- 
tained many tropical forms, I am not sure that this is correct. 
