348 Proceedings of the Royal Irish Academy. 



Navicula gihla, (Ehr.) Fresh, water. 



Yalve nearly linear; very slightly constricted towards the ends, 

 and very gently expanded in the middle. Length about "0044 ; 

 breadth about -0008. Strife finely costate ; convergent in the middle, 

 and radiate towards the ends. Intermediate free space narrow, except 

 in the middle, where it is roundly expanded. (PI. 30, fig. 19.) 



Klitzing, (Bac, p. 98, T. xxviii. fig. 70), has described a form under 

 this name, which he regards as Pinnularia gibba, Ehr. With this the 

 form so named by Eabenhorst (Siissw. Diat., p.45,T.vi., fig. 27), agrees. 

 Ealfs' 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 striae also are parallel, whUe in the present 

 form they are convergent in the middle, and radiate at the ends, just 

 as "VVm. Smith has figured Pinnularia gibba, B. D. Yol. i., 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 E^avi- 

 cula gibba with I^avicula 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, Pathdrum, 

 Co. "Wicklow. Eeatherbed Mountain, Co. Dublin. Lough Moume 

 deposit, Co. Antrim. 



Navicida gMa, var. loechii, (Pab.) Eresh water. 



Yalve smaller than the typical species ; length '0032, breadth 

 •0007; margin very slightly gibbous ; ends somewhat capitate; striae 

 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, Yerhand. 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, Eab. Bacil. Sachs. 



Lough Corrib, Co. Galway. Pond near the city of Armagh. 



Navicula gilha, var. parva, (O'Meara). Eresh water. 



Yalve small; length -0015, breadth -0003; slightly gibbous at the 

 margins ; much attenuated towards the somewhat- capitate ends ; striae 

 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 



