374 Proceedings of the Royal Irish Academy. 



figured by Gnmow as JS'aviciila scopuloriim, in Yerhand. der K. K. Zool. 

 Bot. GeselL, Band x., 1860, p. 547, T. iii. fig. 6. The present species, 

 however, is shorter, broader, and more rhombic ; the transverse striae 

 more obsciire, and not reaching the median line, but leaving a distinct 

 intermediate free space. 



Seaweeds, Dalkey Island, Malahide, Co. Dublin. 



(f) Crassmerves. 



*' Forms for the most part lanceolate, tvith very strong median lines 

 and very fine scarcely noticeahle structure, in which the longitudinal strice 

 come out more distinctly thati the transverse. These approach the group 

 Limosce, from tvhich, hoioever, they differ essentially hy the colorless condi- 

 tion of the valves in a dry state. In the appearance of the median line 

 there is an approximation to some forms of the group CuspidatcB not to he 

 mistaken.^'' — Grunow. 



Navicxda rhomhoides, (Ehr.) Fresh water, 



Yalve rhomboid; lanceolate; ends slightly rounded ; median line 

 distinct, with two longitudinal lines close to and nearly parallel with 

 it ; slightly expanded in the middle, united towards the ends ; the 

 median line extending slightly beyond the point of Junction ; striae 

 very faint ; length about -0045 ; breadth about -0009. (Plate 31, fig. 49.) 



With a high objective and very skilful illumination the striae are 

 found to be parallel. It is noteworthy that in a gathering made by 

 me at Lough Awn, on the summit of the Slieveaneiran Mountain, this 

 form occurred in abundance, for the most part fi-ee, but frequently in 

 mucous tubes, ever in single files, and in some cases the frustules were 

 placed end to end, without any mucous investment. 



Kiitz. Bac, p. 94, T. xxviii., fig. 45 ; and T. xxx., fig. 44. This 

 author attributes the species to Ehrenberg. Wm. Sm., B. D., vol. i., 

 p. 46, PL xvi., fig. 129. Eab. Siissw. Diat., p. 38 ; T. v., fig. 13. This 

 figure represents the form as much smaller than it is generally found 

 to be. Ralfs, in Pritch., p. 903 ; Grunow, Yerhand. der K. K. Zool. 

 Bot. Gesell, Band x., 1860, p. 549. Donkin, I^. H. Brit. Diat., p. 42, 

 PI. vi., fig. 11. Schumann, Die Diat. der Hohen Tatra., p. 68. 



Pool, Glencar, near Glengariff, Bantry, Co. Cork. Lower Lake, 

 Eallarney, Arragien, near Castlegregory, Co. Kerry. Eriarstown, 

 Piperstown, Co. Dublin. Biver Bann, near Coleraine, Co. Derry. Con- 

 nemara, Co. Gal^vay. Bathdrum, Glenchree, Co. Wicklow. Deposit, 

 Tollymore Park, Co. Down. 



Navicula serians, (De'Bx^'h.) Freshwater. 



Yalve elliptical-lanceolate ; ends slightly rounded ; median line dis- 

 tinct, as are also the two longitudinal lines, close to and parallel to the 



