O’Mrara—Report on the Irish Diatomacee. 255 
Orthostra Roeseana, (Rab.) Fresh water. 
Inner surface of cell sub-spherical; frustule sulcate on either side 
of suture; spines at the junction surfaces very distinct and long; cir- 
elet of puncta parallel with suture absent. Strice on side view radiate, 
distinct, with three large puncta placed triangularly at the centre. 
On front view strie finely punctate, and parallel with suture. 
(Pl. 26,-fig. 9.) 
Smith, in 1856, describes this species as new, under the name of 
Orthosira spinosa. Wm. Sm., B. D., Vol. u., p. 62, Pl. lxu., fig. 
386. But it had been already described by Rabenhorst, Siissw. Diat., 
p. 13, T.x., fig. 5, in 1853, as Melosira Roeseana, and with sufficient 
accuracy, both as respects the figure and the description, as to render 
identification certain. Melosira ‘Roeseana, Rallis, 1 m.Pritch.; “p. S18, 
Pl. v., fig. 67: 
Killakee, County Dublin. Ulster Canal, near Poyntzpass. Lough 
Neagh, near Lurgan, County Armagh. Ditch at side of Royal Canal, 
near Kilcock, County Kildare. 
Genus V. Cyctoreria, Kiitz. 
Frustules normally single, narrow ; sometimes slightly waved on 
the front view; on the side view having the valves more or less dis- 
tinectly divided into two concentric portions. 
It is extremely difficult to define this genus by words so precisely as 
to distinguish it with certainty from others nearly allied; yet stall 
the forms included within it constitute a tolerably distinct group. So 
much so, that almost all authors have agreed to mark their peculiarity 
by a distictive generic name. 
Heiberg and Cleve have included the several species under the 
genus Orthosira, with which they are closely allied; but I consider 
them entitled to stand by themselves, not only on account of their 
different modes of growth, but also on account of the distinctive cha- 
racters of their sporangia. 
it would appear at first view that the generic name JDisvoplea 
should, on account of its priority, be preferred to the more recent name 
of Cyclotella. As Ehrenberg has given no verbal diagnosis of his genus 
Discoplea, we have no means of ascertaining its characteristics, other- 
wise than by the figures, and in these no sufficiently distinctive feature 
is discernible. Not only are forms that seem to belong to different 
species included under the same specific name, but more than this, 
species belonging to Orthosira, on the one hand, and more closely re- 
sembling Coscinodiscus, on the other, are included in the genus Disco- 
plea. Kiitzing’s diagnosis of his genus Cyclotella, although sufficient 
to distingush it from Orthosira, on the one hand, is not clear enough, so 
far as words are concerned, to prevent confusion with Coscinodiscus, 
