284 Proceedings of the Royal Irish Academy. 
B.D., Vol. u., p. 17. Pl. xxxiv., fig. 291 ¢., and Fragilaria undata, 
Supp. Pl. lx aera: 
Piperstown, Killikee, Co. Dublin. Verner’s Bridge, Co. Armagh, 
Float bog, Co. Westmeath. 
Wm. Smith has described a form as Odontidium parasiticum, some- 
times expanded in the middle, sometimes constricted, B. D., Vol. 11, 
p. 19, Supp. Pl. lx., 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 Fragilaria. Some few specimens have occa- 
sionally come under my notice, parasitic on Nitzschia 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 Bohernabreena and 
Kallikee, Co. Dublin. 
Fragilaria undata, (Wm. 8m.) Fresh water. 
Valves broad on side view; constricted in the middle; ends attenu- 
ated ; striz strong, persistent. 
Wm. Sm., B.D., Vol. ii., p. 24, Supp. Pl. Ix., fig. 377.—Odonti- 
dium tabellaria, Wm. Sm., B.D., Vol. ii., p. 17; Pl. xxxiv., fig. 291 a.— 
Fragilaria constricta in part, Ralfs, in Pritch., p. 777.—Fragilaria 
virescens var. undata, Grunow, Verhand der K. K. Zool. Bot. Gesel., 
Band xii., 1862, p. 874. Grunow regards this form as likely identical 
with Fragilaria constricta, Ehr. Mic., T. xvi., 2, figs. 84, 35; as also 
with F. 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. 
Bohernabreena, Killikee, Co. Dublin. 
Fragilaria mesolepta, (Rab.) Fresh or brackish water. 
Frustules on front view regularly quadrangular; onside view narrow, 
constricted at the middle, and more slightly constricted towards the 
apices, which are narrowed, produced, and sub-capitate ; stric fine, 
persistent. 
Heiberg, De Danske Diat., p. 61, T. iv., fig. 11.—Fragilaria capu- 
cina var. mesolepta, Rab., Fl. Kur., sect. 1, p. 118. 
Rock pool on sea-shore, Carrickfergus, Co. Antrim. Malahide ; 
Basin, Ringsend, Co. Dublin. 
