394 Proceedings of the Royal Irish Academy. 



Navicula pygmxea, (Klitz..) Marine or brackisli ^vater. 



A^alve linear, elliptical ; marginal band of striae narrow, with a dis- 

 tinct ridge on the inner margin ; inner band of striae relatively broad, 

 reaching the median line, and having a distinct ridge on the outer mar- 

 gin ; striae fine, linear, nearly parallel ; space intermediate between 

 the inner and outer bands of striae narrow, lyi-ate ; apparently un- 

 striate, but on closer inspection it will be found that the striae which 

 seem to be inteiTupted are really pervious; length about -001 5; 

 breadth about '00066, but often of much larger dimensions. (Plate 

 33, fig. 7.) 



Wm. Smith (B. D., Yol. ii., p. 91), who attributes the species to 

 Kiitzing. Rabenhorst (Siissw. Diat., p. 39) refers to a form under this- 

 name without a figure ; the species is not correctly included among 

 those incidental to fi'esh water. E,alf s, in Pritch. , p. 899, who says ' ' the 

 species occurs in brackish or fresh water ; " but though often found by me 

 in marine gatherings, it never once occurred to me in fi-esh water. 

 Donkin, J^. H. Brit. Diat. p. 10, PL i., fig. 10. Lagerstedt, Sotvat. 

 Diat. friin Spetzbergen dch Beeren Eiland, p. 27. — yavicula minutula, 

 "Wm.Sm.,B.D., Yol i., p. 48, PI. xxxi., fig. 274. 



Bannow, salt ditch near town of "Wexford, PJver Slaney, near 

 Xillurin, Tacumshane, Co. Y^exford. Malahide, Portmarnock, Piles 

 of wooden bridge, Dollymount Strand, Co. "Dublin. Galway Bay, 

 near town of Galway. Portnacrush, Co. Donegal. Lough Gill, Co. 

 Kerry. On seaweeds, Kilkee, Co. Clare. 



Yar. cuneata, (0'!Meara). ITarine. 

 Yalve linear, elliptical, with cuneate ends; marginal band of striae 

 broad ; inner band of striae narrow ; striae coarse, linear, distant, 

 parallel in the middle, slightly radiate towards the ends, lyrate ; 

 fi'ee space narrow, and sometimes difficult to detect; length "0017: 

 breadth -0010. (Plate 33, fig. 8.) 



Stomachs of Ascidians, Broadhavcn Bay, Co. Galway. 



(k) Trifasciatce. 



Distinguishecl ly having tlie intermediate space letween the inner mar- 

 gins of the marginal lands of strice divided into three distinct longitudinal 

 compartments, one aloict the median line, and one on either side of the same. 



f Not constricted in the middle. 



Navicida expleta. ~^. S. lEarinc. 



Yalve broadly elliptical ; median compartment nearly linear, 

 slightly incurved towards the ends, next compartments narrow,, 

 lunate ; marginal band of striae relatively wide ; striae linear, undu- 

 late, divided by about five longitudinal sulci; length about -0018 j 

 breadth about -0012. (Plate 33,''fig. 9.) 



This form appears to me obviously identical with that described 



