270 Proceedings of the Royal Irish Academy. 
Genus XIII. Avtiscus, Ehr. 
Surface of the valve undulate, furnished with two large processes; 
strie plumose, arranged in form of a quatrefoil. 
Auliscus sculptus, (Wm. Sm.) Marine. 
Strive linear. (PI. 27, fig. 4.) 
Ralfs, in Pritch., p. 845, Pl. vi., fig. 3. Greville, Q.J.M:S., 
1863, p. 43, Pl. ii., figs. 1-8. Heiberg, De Danske Diat., p. 37. 
Cleve, Om Svenska och Norska Diat., p. 218.—Eupodiscus sculptus, 
Wm. Sm., B.D., Vol. 1., p. 25, Pl. iv., fig. 42.—Aulacodiscus sculp- 
tus, Brightwell, Q.J.M.8., 1860, p. 94, Pl. v., fig. 3. 
Malahide. Piles of wooden bridge, Dollymount, Co. Dublin. River 
Slaney, at Killurin, Co. Wexford. Sea-weeds, near town of Wicklow. 
Westport, Co. Galway. 
Genus XIV. Oponroprscus, Ehr, 
Disk furnished with marginal teeth. 
In this genus I have united Ehrenberg’s two genera, Odontodiscus 
and Systephania, deeming the distinction between them not of suffi- 
cient importance to justify their separation. The distinction, as ex- 
pressed by Ralfs, is simply this, that in Odontodiscus ‘‘ the dots are 
radiate, not parallel, as in Systephania.”’ 
Odontodiscus excentricus, (Ehr.) Marine. 
Disk varying in size from ‘0008 to °0025 ; areolate; areoles round, 
arranged in curved excentric lines; teeth numerous, short. (Pl. 27, 
fig. 5. 
° Ele Mic.,.T, xxxv.,:A.:18; fig. 11,-- Ralis, im. Priteh. i Bee. 
Pl. v., fig. 90.—Coscinodiscus excentricus, Kiitz. Bac., p. 131, T.i., 
fig. 9, in which the teeth are not figured or described. Wm. Sm., 
B.D., Vol. i., p. 23, Pl. ii., fig. 38.—Eupodiscus excentricus, O’M., 
Q.J.M.S8., 1867, p. 249, Pl. vii., fig. 2. 
Sea-weeds, Bannow. Salt ditch near Wexford. Piles of wooden 
bridge, Dollymount, Malahide, Stomachs of Pectens, Dalkey, from 
Corallines, Howth, Sea-weeds, Ballybrack, Co. Dublin. Sea-weeds, 
Kilkee, Stomachs of Ascidians, Co. Clare. Stomachs of Ascidians, 
Roundstone Bay, Co. Galway. 
Odontodiscus anglicus, (Donkin.) Marine. 
Disk about ‘0016 in diameter ; teeth large and prominent, occupy- 
ing a tolerably broad unstriate margin; stria minutely punctate, decus- 
sately arranged. (PI. 27, fig. 6). 
