284 Proceedings of the Royal Irish Academy. 



B. D., Yol. ii., p. 17. PI. xxxiv., fig. 291 a., and Pragilaria undata, 

 Supp. PL Ix., fig. 377 a. 



Piperstown, Killikee, Co, Dublin. Yerner's Bridge, Co. Armagh, 

 Ploat bog, Co. Westmeath. 



"Wm. Smith, has described a form as Odontidium parasiticum, some- 

 times expanded in the middle, sometimes constricted, B. D., Yol, ii., 

 p. 19, Supp. PI. Ix., fig. 375. The separate valves of the latter would 

 seem to be a variety of the following species, those of the former to 

 belong to the present ; the habit of growth, however, is much more 

 that of Synedra than of Pragilaria, Some few specimens have occa- 

 sionally come under my notice, parasitic on Mtzschia sigmoidea, and in 

 no way differing from the representation in Smith's figure. So seldom, 

 however, did they occur, and in such small quantity, I never could 

 make any satisfactory examination of them, and therefore refer to 

 the subject here in deference to the opinions of the best authors, who 

 have placed them in the genus Fragilaria — not because I agree with 

 them in considering such is their proper place, but because I consider 

 it inexpedient to make any change until an opportunity for more 

 thorough examination shall have been afforded. 



The forms have occurred in gatherings from Bohemabreena and 

 KiUikee, Co. DubHn, 



Fragilaria undata, ("Wm. Sm.) Fresh water. 

 Yalves broad on side view ; constricted in the middle ; ends attenu- 

 ated ; striae strong, persistent. 



Wm. Sm., B. D., Yol. ii., p. 24, Supp. PI. Ix., fig. 377.— Odonti- 

 dium tabellaria, Wm. Sm., B.D., Yol. ii., p. 17; PI. xxxiv., fig. 291 a. — 

 Pragilaria constricta in part, Ealfs, in Pritch., p, 777. — Pragilaria 

 virescens var. undata, Grunow, Yerhand der K. K. Zool. Bot. Gresel., 

 Band xii., 1862, p. 374. Grunow regards this form as likely identical 

 with Fragilaria constricta, Ehr. Mic, T. xvi., 2, figs. 34, 35 ; as also 

 with P. binodis, Ehr. Mic, T. vi. 1, fig. 43; but as there is some 

 doubt on this point, and as some of the figures of the forms so named 

 appear to be incorrectly attributed to this species, it is better to refer 

 the species to Wm. Smith, whose figure admits of no doubt, 



Bohemabreena, Killikee, Co. Dublin. 



Fragilaria mesolepta, (Rab.) Presh or brackish water. 



Prustules on front view regularly quadi'angular ; on side view narrow, 

 constricted at the middle, and more slightly constricted towards the 

 apices, which are narrowed, produced, and sub-capitate ; striae fine, 

 persistent. 



Heiberg, De Danske Diat., p. 61, T. iv., fig. 11. — Pragilaria capu- 

 <;ina var. mesolepta, Rab., El. Eur., sect. 1, p. 118. 



Rock pool on sea-shore, Carrickfergus, Co. Antrim. IMalahide ; 

 IBasin, Ringsend, Co. Dublin. 



