348 Proceedings of the Royal Irish Academy. 
Navicula gibba, (Ehr.) Fresh water. 
Valve nearly linear; very slightly constricted towards the ends, 
and very gently expanded in the middle. Length about ‘0044; 
breadth about :0008. Strie finely costate; convergent in the middle, 
and radiate towards the ends. Intermediate free space narrow, except 
in the middle, where it is roundly expanded. (Pl. 30, fig. 19.) 
Kiitzing, (Bac., p. 98, T. xxvii. fig. 70), has described a form under 
this name, which he regards as Pinnularia gibba, Ehr. With this the 
form so named by Rabenhorst (Stssw. Diat., p.45, T.vi., fig. 27), agrees. 
Ralfs’ description seems tolerably well to correspond, ‘‘ lanceolate, 
with dilated capitate ends.’’ In the above cases the figures represent 
the form more gibbous in the middle than the present species, and 
with capitate ends; the striz also are parallel, while in the present 
form they are convergent in the middle, and radiate at the ends, just 
as Wm. Smith has figured Pinnularia gibba, B. D. Vol. 1., p. 58, Pl. 
xix., fig. 180. The present form is less capitate at the ends, and the 
intermediate free space more roundly expanded in the middle than in 
Smith’s figure. Grunow, comparing the species he has named Navi- 
cula gibba with Nayicula tabellaria, says it stands distinct from it ‘‘ by 
the narrower expansion of the ends, and the more gradual tapering in. 
the middle.’”’ Verhand. der K. K. Zool. Bot. Gesell., Band x., 1860, 
p. 517. This description corresponds exactly with the present form. 
Lough Corrib, Co. Galway. Drumoughty Lough, near Kenmare, 
Co. Cork. Carn Lough, near Tralee, Co. Kerry. Derrylane Lough, 
Co. Cavan. Carrickmacreely Hill, Lugnaquilla Mountain, Rathdrum, 
Co. Wicklow. Featherbed Mountain, Co. Dublin. Lough Mourne 
deposit, Co. Antrim. 
Nawicula gibba, var. boeckit, (Rab.) Fresh water. 
Valve smaller than the typical species; length °0032, breadth 
‘0007; margin very slightly gibbous; ends somewhat capitate; strie 
finely costate; intermediate free space narrow, except at the middle, 
where it expands considerably, sometimes reaching the margin at one 
side, but not at the other. (Plate 30, fig. 20.) 
Grunow, Verhand. der K. K. Zool. Bot. Gesell., Band x., 1860, 
p. 517, T. iv., fig. 17. This author regards the form as identical with 
Staurophora peckii, Rab. Bacil. Sachs. 
Lough Corrib, Co. Galway. Pond near the city of Armagh. 
Navicula gibba, var. parva, (O'Meara). Fresh water. 
Valve small; length -0015, breadth :0003; slightly gibbous at the 
margins; much attenuated towards the somewhat-capitate ends; strie 
costate, fine, convergent in the middle, and slightly radiate towards the 
ends; intermediate free space relatively broad, expanding at the 
middle, and sometimes reaching to the margin. (Plate 30, fig. 21.) 
There is a form somewhat. similar to this described by Grunow 
