O'Meara — Report on the Irish Biatomaccce. 359 



Nmicula decipiens, l!^. S. Marine. 



Valve narro-u^, elliptical, rounded at ends ; length '0030, breadth 

 •0008. Strise fine, close, slightly radiate ; in some lights apparently 

 punctate ; seemingly disappearing in the middle, and presenting the 

 appearance of a narrow stanroform band, extending to the margins ; 

 this however is deceptive. (PI. 31, fig. 6.) 



Tide-pools, Galway Bay, near the town of Galway. 



Nmicnla tumens. ("Wm. Smith). Brackish or marine. 



Yalve elliptical; ends produced. Length from -0024 to -0040, 

 breadth from -0010 to -0015. Striae fine, punctate, slightly radiate ; 

 vrhen not exactly in focus appearing to be moniliform. (PI. 31, fig. 7.) 



Smith has correctly described the character of the strise in this 

 species ; but the figure represents the striae as they appear when not 

 in fociis. 



Dentin, IST. H., Brit. Diat., p. 15, considers this form as identical 

 with K"avicula rostrata, Ehr., and JSTavicula sculpta, Ehr. These 

 forms it appears were found by Donkin in the Bergmehl of Santa 

 Eiore, and in the fossil deposit of Eranzensbad, which I believe are 

 both fresh water deposits, thoiigh that author assigns [N'avicula ros- 

 trata to brackish localities. The form under consideration has been 

 found by Smith only in brackish water ; and I have found it only in 

 localities decidedly brackish or marine. However similar the forms 

 may be, they seem to mc perfectly distinct, and distinguishable by 

 this feature, that in J^avicula tumens the striae run uninterruptedly 

 from the margin to the longitudinal sulci, whereas in JST. rostrata they 

 are interrupted, and present an unstriate space between each sulcus 

 and the ends of the stria3. AYm. Sm., B. D., Vol. i., p. 52, PI. xvii., 

 fig. 150. Ealfs, in Pritch., p. 900. Grunow, Verhand. der K. K. Zool. 

 Bot. GeselL, Band x., 1860, p. 541. Rab. El. Eur. Alg., sect, i., p. 192. 



Salt ditch, near ISTewtownliraavady Junction, Co. Londonderry. 

 Salt ditch, near the town of Galway. Seaweeds, Salt Hill, Co. 

 Dublin. Salt ditch. Breaches, Co. Wicklow. Lough Gill, Co. Kerry. 



Navicula rostrata. (Ehr.) Ercsh or brackish water. 



Yalves elliptical, produced into long rounded apices ; length 

 •0046, breadth '0015. Striae punctate, slightly radiate, disappearing 

 in the middle of the space between the margin and the longitudinal 

 sulcus, and appearing again upon the edge of the sulcus. (PI. 31, fig. 8.) 

 There is some doubt as to whether this species belongs to fresh 

 or brackish water. The fact that Donkin identified the form, so well 

 delineated by him, with specimens from the Santa Eiore deposit, as well 

 as that of Eranzensbad, would seem decisive as to its proper habitat 

 being in fresh water. The localities, however, to which he has 

 assigned the species found by him in a living state are brackish ; 



