290 Proceedings of the Royal Irish Academy. 
very narrow. ‘This species is very much larger than the species here- 
tofore described. 
Ralfs, in Pritch., p. 790. Rab. Fl. Eur., sect. 1, p. 124.—Denti- 
cula marina, Gregory, Diat. of Clyde, p. 24, Pl. x., fig. 39. 
From stomachs of Ascidians, Roundstone Bay, Co. Galway. Sea- 
weeds, near the Newtownlimavady junction, Co. Derry. 
Genus VY. PragiogRAmMMa, Grey. 
Frustules similar to those of the preceding genus, from which they 
are distinguished by the presence of a pair of strong, transverse coste, 
including a central unstriate band. Some of the species have also, 
besides, a similar terminal costa at either end, the space between 
which and the apex is unstriate ; valves striate, except at the central 
and terminal portions referred to; striz sometimes interrupted in the 
middle, sometimes persistent ; filaments short. 
Plagiogramma staurophorum, (Greg.) Marine. 
Valves furnished with a central pair of transverse, pervious cost; 
on front view margin slightly dilated ; on side view elliptical, obtuse ; 
strie fine, moniliform, persistent; central cost inflexed; the unstri- 
ate band bounded by the same, narrow, and extending across the valve, 
from margin to margin. 
Heiberg, De Danske Diat., p. 165. Cleve, Om Svenska och Norska 
Diat., p. 219.—Denticula staurophora, Gregory, Diat. of Clyde, p. 24, 
Pl. x., fig. 37. Plagiogramma Gregorianun, Grev., Q.J.M.S8., July, 
1859, p. 208, Pl. x., figs. 1 and 2. Rallis, m Pritch.<p) 774.4 Rap: 
ie lpr sect. ep. lle 
On piles of wooden bridge, Dollymount, Oyster beds, Malahide, 
Co. Dublin. Sea-weeds, near Newtownlimavady junction, Co. Derry. 
Sea-weeds, Bannow, Co. Wexford. From stomachs of Ascidians, 
Roundstone Bay, Co. Galway. 
Plagiogramma costatum, (O’M.) Marine. 
Valves furnished with both a central pair of costz and a single 
costa at either end; frustules in front view quadrangular; terminal 
constriction slight; on side view central and terminal cost inflexed; 
valve broadly elliptical, with slightly-cuneate ends; central unstriate 
band extending across the valve; striz costate; coste pervious. (Pl. 
27, fig. 20.) 
O’Meara, Q. J. M.S., April, 1869, p. 150, Pl. xa.) fig. 2: 
Arran Islands, Co. Galway. 
